diff --git a/application/Espo/Classes/Acl/Email/AssignmentChecker.php b/application/Espo/Classes/Acl/Email/AssignmentChecker.php
new file mode 100644
index 0000000000..fbe58e4642
--- /dev/null
+++ b/application/Espo/Classes/Acl/Email/AssignmentChecker.php
@@ -0,0 +1,51 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Classes\Acl\Email;
+
+use Espo\Entities\User;
+
+use Espo\ORM\Entity;
+
+use Espo\Core\{
+    Acl\AssignmentChecker\DefaultAssignmentChecker,
+};
+
+class AssignmentChecker extends DefaultAssignmentChecker
+{
+    protected function isPermittedAssignedUser(User $user, Entity $entity): bool
+    {
+        return true;
+    }
+
+    protected function isPermittedAssignedUsers(User $user, Entity $entity): bool
+    {
+        return true;
+    }
+}
diff --git a/application/Espo/Core/Acl/AssignmentChecker.php b/application/Espo/Core/Acl/AssignmentChecker.php
new file mode 100644
index 0000000000..b40a8ff272
--- /dev/null
+++ b/application/Espo/Core/Acl/AssignmentChecker.php
@@ -0,0 +1,42 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\Acl;
+
+use Espo\ORM\Entity;
+
+use Espo\Entities\User;
+
+interface AssignmentChecker
+{
+    /**
+     * Check assignment.
+     */
+    public function check(User $user, Entity $entity): bool;
+}
diff --git a/application/Espo/Core/Acl/AssignmentChecker/AssignmentCheckerFactory.php b/application/Espo/Core/Acl/AssignmentChecker/AssignmentCheckerFactory.php
new file mode 100644
index 0000000000..75ec59b7df
--- /dev/null
+++ b/application/Espo/Core/Acl/AssignmentChecker/AssignmentCheckerFactory.php
@@ -0,0 +1,86 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\Acl\AssignmentChecker;
+
+use Espo\Core\{
+    Utils\ClassFinder,
+    Utils\Metadata,
+    InjectableFactory,
+    Acl\AssignmentChecker,
+    Acl\Exceptions\NotImplemented,
+};
+
+class AssignmentCheckerFactory
+{
+    private $defaultClassName = DefaultAssignmentChecker::class;
+
+    private $classFinder;
+
+    private $metadata;
+
+    private $injectableFactory;
+
+    public function __construct(
+        ClassFinder $classFinder,
+        Metadata $metadata,
+        InjectableFactory $injectableFactory
+    ) {
+        $this->classFinder = $classFinder;
+        $this->metadata = $metadata;
+        $this->injectableFactory = $injectableFactory;
+    }
+
+    /**
+     * Create an access checker.
+     *
+     * @throws NotImplemented
+     */
+    public function create(string $scope): AssignmentChecker
+    {
+        $className = $this->getClassName($scope);
+
+        return $this->injectableFactory->create($className);
+    }
+
+    private function getClassName(string $scope): string
+    {
+        $className = $this->metadata->get(['aclDefs', $scope, 'assignmentCheckerClassName']);
+
+        if ($className) {
+            return $className;
+        }
+
+        if (!$this->metadata->get(['scopes', $scope])) {
+            throw new NotImplemented();
+        }
+
+        return $this->defaultClassName;
+    }
+}
diff --git a/application/Espo/Core/Acl/AssignmentChecker/AssignmentCheckerManager.php b/application/Espo/Core/Acl/AssignmentChecker/AssignmentCheckerManager.php
new file mode 100644
index 0000000000..85fb73b36a
--- /dev/null
+++ b/application/Espo/Core/Acl/AssignmentChecker/AssignmentCheckerManager.php
@@ -0,0 +1,78 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\Acl\AssignmentChecker;
+
+use Espo\ORM\Entity;
+
+use Espo\Entities\User;
+
+use Espo\Core\{
+    Utils\Metadata,
+    Acl\AssignmentChecker,
+};
+
+class AssignmentCheckerManager
+{
+    private $checkerCache = [];
+
+    private $metadata;
+
+    private $factory;
+
+    public function __construct(Metadata $metadata, AssignmentCheckerFactory $factory)
+    {
+        $this->metadata = $metadata;
+        $this->factory = $factory;
+    }
+
+    public function check(User $user, Entity $entity): bool
+    {
+        $entityType = $entity->getEntityType();
+
+        $checker = $this->getChecker($entityType);
+
+        return $checker->check($user, $entity);
+    }
+
+    private function getChecker(string $entityType): AssignmentChecker
+    {
+
+        if (!array_key_exists($entityType, $this->checkerCache)) {
+            $this->loadChecker($entityType);
+        }
+
+        return $this->checkerCache[$entityType];
+    }
+
+    private function loadChecker(string $entityType): void
+    {
+        $this->checkerCache[$entityType] = $this->factory->create($entityType);
+    }
+}
diff --git a/application/Espo/Core/Acl/AssignmentChecker/DefaultAssignmentChecker.php b/application/Espo/Core/Acl/AssignmentChecker/DefaultAssignmentChecker.php
new file mode 100644
index 0000000000..c162b49c99
--- /dev/null
+++ b/application/Espo/Core/Acl/AssignmentChecker/DefaultAssignmentChecker.php
@@ -0,0 +1,353 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\Acl\AssignmentChecker;
+
+use Espo\ORM\{
+    Entity,
+    EntityManager,
+    Defs\Defs,
+};
+
+use Espo\Entities\User;
+
+use Espo\Core\{
+    AclManager,
+    Acl\AssignmentChecker,
+    Acl\Table,
+};
+
+class DefaultAssignmentChecker implements AssignmentChecker
+{
+    protected const FIELD_ASSIGNED_USERS = 'assignedUsers';
+
+    protected const FIELD_TEAMS = 'teams';
+
+    protected const ATTR_ASSIGNED_USER_ID = 'assignedUserId';
+
+    protected const ATTR_TEAMS_IDS = 'teamsIds';
+
+    protected const ATTR_ASSIGNED_USERS_IDS = 'assignedUsersIds';
+
+    private $aclManager;
+
+    private $entityManager;
+
+    private $ormDefs;
+
+    public function __construct(AclManager $aclManager, EntityManager $entityManager, Defs $ormDefs)
+    {
+        $this->aclManager = $aclManager;
+        $this->entityManager = $entityManager;
+        $this->ormDefs = $ormDefs;
+    }
+
+    public function check(User $user, Entity $entity): bool
+    {
+        if (!$this->isPermittedAssignedUser($user, $entity)) {
+            return false;
+        }
+
+        if (!$this->isPermittedTeams($user, $entity)) {
+            return false;
+        }
+
+        if ( $this->hasAssignedUsersField($entity->getEntityType())) {
+            if (!$this->isPermittedAssignedUsers($user, $entity)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private function hasAssignedUsersField(string $entityType): bool
+    {
+        $entityDefs = $this->ormDefs->getEntity($entityType);
+
+        return
+            $entityDefs->hasField(self::FIELD_ASSIGNED_USERS) &&
+            $entityDefs->getField(self::FIELD_ASSIGNED_USERS)->getType() === 'linkMultiple' &&
+            $entityDefs->hasRelation(self::FIELD_ASSIGNED_USERS) &&
+            $entityDefs->getRelation(self::FIELD_ASSIGNED_USERS)->getForeignEntityType() === 'User';
+    }
+
+    protected function isPermittedAssignedUser(User $user, Entity $entity): bool
+    {
+        if (!$entity->hasAttribute(self::ATTR_ASSIGNED_USER_ID)) {
+            return true;
+        }
+
+        $assignedUserId = $entity->get(self::ATTR_ASSIGNED_USER_ID);
+
+        if ($user->isPortal()) {
+            if (!$entity->isAttributeChanged(self::ATTR_ASSIGNED_USER_ID) && !$assignedUserId) {
+                return true;
+            }
+
+            return false;
+        }
+
+        $assignmentPermission = $this->aclManager->getPermissionLevel($user, 'assignmentPermission');
+
+        if (
+            $assignmentPermission === Table::LEVEL_YES ||
+            !in_array($assignmentPermission, [Table::LEVEL_TEAM, Table::LEVEL_NO])
+        ) {
+            return true;
+        }
+
+        $toProcess = false;
+
+        if (!$entity->isNew()) {
+            if ($entity->isAttributeChanged(self::ATTR_ASSIGNED_USER_ID)) {
+                $toProcess = true;
+            }
+        }
+        else {
+            $toProcess = true;
+        }
+
+        if (!$toProcess) {
+            return true;
+        }
+
+        if (empty($assignedUserId)) {
+            if ($assignmentPermission === Table::LEVEL_NO && !$user->isApi()) {
+                return false;
+            }
+
+            return true;
+        }
+
+        if ($assignmentPermission === Table::LEVEL_NO) {
+            if ($user->id !== $assignedUserId) {
+                return false;
+            }
+        }
+        else if ($assignmentPermission === Table::LEVEL_TEAM) {
+            $teamIdList = $user->get(self::ATTR_TEAMS_IDS);
+
+            if (
+                !$this->entityManager
+                    ->getRepository('User')
+                    ->checkBelongsToAnyOfTeams($assignedUserId, $teamIdList)
+            ) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    protected function isPermittedTeams(User $user, Entity $entity): bool
+    {
+        $assignmentPermission = $this->aclManager->getPermissionLevel($user, 'assignmentPermission');
+
+        if (!in_array($assignmentPermission, [Table::LEVEL_TEAM, Table::LEVEL_NO])) {
+            return true;
+        }
+
+        if (!$entity->hasLinkMultipleField(self::FIELD_TEAMS)) {
+            return true;
+        }
+
+        $teamIdList = $entity->getLinkMultipleIdList(self::FIELD_TEAMS);
+
+        if (empty($teamIdList)) {
+            return $this->isPermittedTeamsEmpty($user, $entity);
+        }
+
+        $newIdList = [];
+
+        if (!$entity->isNew()) {
+            $existingIdList = [];
+
+            $teamCollection = $this->entityManager
+                ->getRDBRepository($entity->getEntityType())
+                ->getRelation($entity, self::FIELD_TEAMS)
+                ->select('id')
+                ->find();
+
+            foreach ($teamCollection as $team) {
+                $existingIdList[] = $team->getId();
+            }
+
+            foreach ($teamIdList as $id) {
+                if (!in_array($id, $existingIdList)) {
+                    $newIdList[] = $id;
+                }
+            }
+        }
+        else {
+            $newIdList = $teamIdList;
+        }
+
+        if (empty($newIdList)) {
+            return true;
+        }
+
+        $userTeamIdList = $user->getLinkMultipleIdList(self::FIELD_TEAMS);
+
+        foreach ($newIdList as $id) {
+            if (!in_array($id, $userTeamIdList)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private function isPermittedTeamsEmpty(User $user, Entity $entity): bool
+    {
+        $assignmentPermission = $this->aclManager->getPermissionLevel($user, 'assignmentPermission');
+
+        if ($assignmentPermission !== Table::LEVEL_TEAM) {
+            return true;
+        }
+
+        if ($entity->hasLinkMultipleField(self::FIELD_ASSIGNED_USERS)) {
+            $assignedUserIdList = $entity->getLinkMultipleIdList(self::FIELD_ASSIGNED_USERS);
+
+            if (empty($assignedUserIdList)) {
+                return false;
+            }
+        }
+        else if ($entity->hasAttribute(self::ATTR_ASSIGNED_USER_ID)) {
+            if (!$entity->get(self::ATTR_ASSIGNED_USER_ID)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    protected function isPermittedAssignedUsers(User $user, Entity $entity): bool
+    {
+        if (!$entity->hasLinkMultipleField(self::FIELD_ASSIGNED_USERS)) {
+            return true;
+        }
+
+        if ($user->isPortal()) {
+            if (count($entity->getLinkMultipleIdList(self::FIELD_ASSIGNED_USERS)) === 0) {
+                return true;
+            }
+        }
+
+        $assignmentPermission = $this->aclManager->getPermissionLevel($user, 'assignmentPermission');
+
+        if (
+            $assignmentPermission === Table::LEVEL_YES ||
+            !in_array($assignmentPermission, [Table::LEVEL_TEAM, Table::LEVEL_NO])
+        ) {
+            return true;
+        }
+
+        $toProcess = false;
+
+        if (!$entity->isNew()) {
+            $userIdList = $entity->getLinkMultipleIdList(self::FIELD_ASSIGNED_USERS);
+
+            if ($entity->isAttributeChanged(self::ATTR_ASSIGNED_USERS_IDS)) {
+                $toProcess = true;
+            }
+        }
+        else {
+            $toProcess = true;
+        }
+
+        $userIdList = $entity->getLinkMultipleIdList(self::FIELD_ASSIGNED_USERS);
+
+        if (!$toProcess) {
+            return true;
+        }
+
+        if (empty($userIdList)) {
+            if ($assignmentPermission === Table::LEVEL_NO && !$user->isApi()) {
+                return false;
+            }
+
+            return true;
+        }
+
+        if ($assignmentPermission === Table::LEVEL_NO) {
+            return $this->isPermittedAssignedUsersLevelNo($user, $entity);
+        }
+
+        if ($assignmentPermission === Table::LEVEL_TEAM) {
+            return $this->isPermittedAssignedUsersLevelTeam($user, $entity);
+        }
+
+        return true;
+    }
+
+    private function isPermittedAssignedUsersLevelNo(User $user, Entity $entity): bool
+    {
+        $userIdList = $entity->getLinkMultipleIdList(self::FIELD_ASSIGNED_USERS);
+
+        $fetchedAssignedUserIdList = $entity->getFetched(self::ATTR_ASSIGNED_USERS_IDS);
+
+        foreach ($userIdList as $userId) {
+            if (!$entity->isNew() && in_array($userId, $fetchedAssignedUserIdList)) {
+                continue;
+            }
+
+            if ($user->getId() !== $userId) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private function isPermittedAssignedUsersLevelTeam(User $user, Entity $entity): bool
+    {
+        $userIdList = $entity->getLinkMultipleIdList(self::FIELD_ASSIGNED_USERS);
+
+        $fetchedAssignedUserIdList = $entity->getFetched(self::ATTR_ASSIGNED_USERS_IDS);
+
+        $teamIdList = $user->getLinkMultipleIdList(self::FIELD_TEAMS);
+
+        foreach ($userIdList as $userId) {
+            if (!$entity->isNew() && in_array($userId, $fetchedAssignedUserIdList)) {
+                continue;
+            }
+
+            if (
+                !$this->entityManager
+                    ->getRepository('User')
+                    ->checkBelongsToAnyOfTeams($userId, $teamIdList)
+            ) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}
diff --git a/application/Espo/Core/Di/AssignmentCheckerManagerAware.php b/application/Espo/Core/Di/AssignmentCheckerManagerAware.php
new file mode 100644
index 0000000000..bae031c54c
--- /dev/null
+++ b/application/Espo/Core/Di/AssignmentCheckerManagerAware.php
@@ -0,0 +1,37 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\Di;
+
+use Espo\Core\Acl\AssignmentChecker\AssignmentCheckerManager;
+
+interface AssignmentCheckerManagerAware
+{
+    public function setAssignmentCheckerManager(AssignmentCheckerManager $assignmentCheckerManager): void;
+}
diff --git a/application/Espo/Core/Di/AssignmentCheckerManagerSetter.php b/application/Espo/Core/Di/AssignmentCheckerManagerSetter.php
new file mode 100644
index 0000000000..f317e7b45b
--- /dev/null
+++ b/application/Espo/Core/Di/AssignmentCheckerManagerSetter.php
@@ -0,0 +1,45 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\Di;
+
+use Espo\Core\Acl\AssignmentChecker\AssignmentCheckerManager;
+
+trait AssignmentCheckerManagerSetter
+{
+    /**
+     * @var AssignmentCheckerManager
+     */
+    protected $assignmentCheckerManager;
+
+    public function setAssignmentCheckerManager(AssignmentCheckerManager $assignmentCheckerManager): void
+    {
+        $this->assignmentCheckerManager = $assignmentCheckerManager;
+    }
+}
diff --git a/application/Espo/Core/Record/Service.php b/application/Espo/Core/Record/Service.php
index 82d80c7703..07cd15afad 100644
--- a/application/Espo/Core/Record/Service.php
+++ b/application/Espo/Core/Record/Service.php
@@ -84,7 +84,8 @@ class Service implements Crud,
     Di\FieldUtilAware,
     Di\FieldValidationManagerAware,
     Di\RecordServiceContainerAware,
-    Di\SelectBuilderFactoryAware
+    Di\SelectBuilderFactoryAware,
+    Di\AssignmentCheckerManagerAware
 {
     use Di\ConfigSetter;
     use Di\ServiceFactorySetter;
@@ -97,6 +98,7 @@ class Service implements Crud,
     use Di\FieldValidationManagerSetter;
     use Di\RecordServiceContainerSetter;
     use Di\SelectBuilderFactorySetter;
+    use Di\AssignmentCheckerManagerSetter;
 
     protected $getEntityBeforeUpdate = false;
 
@@ -364,253 +366,21 @@ class Service implements Crud,
     }
 
     /**
-     * @return void
      * @throws Forbidden
      */
-    public function processAssignmentCheck(Entity $entity)
+    protected function processAssignmentCheck(Entity $entity): void
     {
         if (!$this->checkAssignment($entity)) {
             throw new Forbidden("Assignment failure: assigned user or team not allowed.");
         }
     }
 
+    /**
+     * Check whether assignment can be applied for an entity.
+     */
     public function checkAssignment(Entity $entity): bool
     {
-        if (!$this->isPermittedAssignedUser($entity)) {
-            return false;
-        }
-
-        if (!$this->isPermittedTeams($entity)) {
-            return false;
-        }
-
-        if ($entity->hasLinkMultipleField('assignedUsers')) {
-            if (!$this->isPermittedAssignedUsers($entity)) {
-                return false;
-            }
-        }
-
-        return true;
-    }
-
-    public function isPermittedAssignedUsers(Entity $entity): bool
-    {
-        if (!$entity->hasLinkMultipleField('assignedUsers')) {
-            return true;
-        }
-
-        if ($this->user->isPortal()) {
-            if (count($entity->getLinkMultipleIdList('assignedUsers')) === 0) {
-                return true;
-            }
-        }
-
-        $assignmentPermission = $this->acl->get('assignmentPermission');
-
-        if (
-            $assignmentPermission === true ||
-            $assignmentPermission === AclTable::LEVEL_YES ||
-            !in_array($assignmentPermission, [AclTable::LEVEL_TEAM, AclTable::LEVEL_NO])
-        ) {
-            return true;
-        }
-
-        $toProcess = false;
-
-        if (!$entity->isNew()) {
-            $userIdList = $entity->getLinkMultipleIdList('assignedUsers');
-
-            if ($entity->isAttributeChanged('assignedUsersIds')) {
-                $toProcess = true;
-            }
-        }
-        else {
-            $toProcess = true;
-        }
-
-        $userIdList = $entity->getLinkMultipleIdList('assignedUsers');
-
-        if ($toProcess) {
-            if (empty($userIdList)) {
-                if ($assignmentPermission == AclTable::LEVEL_NO && !$this->user->isApi()) {
-                    return false;
-                }
-
-                return true;
-            }
-
-            $fetchedAssignedUserIdList = $entity->getFetched('assignedUsersIds');
-
-            if ($assignmentPermission === AclTable::LEVEL_NO) {
-                foreach ($userIdList as $userId) {
-                    if (!$entity->isNew() && in_array($userId, $fetchedAssignedUserIdList)) {
-                        continue;
-                    }
-
-                    if ($this->user->id != $userId) {
-                        return false;
-                    }
-                }
-            } else if ($assignmentPermission === AclTable::LEVEL_TEAM) {
-                $teamIdList = $this->user->getLinkMultipleIdList('teams');
-
-                foreach ($userIdList as $userId) {
-                    if (!$entity->isNew() && in_array($userId, $fetchedAssignedUserIdList)) {
-                        continue;
-                    }
-
-                    if (
-                        !$this->entityManager
-                            ->getRepository('User')
-                            ->checkBelongsToAnyOfTeams($userId, $teamIdList)
-                    ) {
-                        return false;
-                    }
-                }
-            }
-        }
-
-        return true;
-    }
-
-    public function isPermittedAssignedUser(Entity $entity): bool
-    {
-        if (!$entity->hasAttribute('assignedUserId')) {
-            return true;
-        }
-
-        $assignedUserId = $entity->get('assignedUserId');
-
-        if ($this->user->isPortal()) {
-            if (!$entity->isAttributeChanged('assignedUserId') && empty($assignedUserId)) {
-                return true;
-            }
-        }
-
-        $assignmentPermission = $this->acl->get('assignmentPermission');
-
-        if (
-            $assignmentPermission === true ||
-            $assignmentPermission === AclTable::LEVEL_YES ||
-            !in_array($assignmentPermission, [AclTable::LEVEL_TEAM, AclTable::LEVEL_NO])
-        ) {
-            return true;
-        }
-
-        $toProcess = false;
-
-        if (!$entity->isNew()) {
-            if ($entity->isAttributeChanged('assignedUserId')) {
-                $toProcess = true;
-            }
-        } else {
-            $toProcess = true;
-        }
-
-        if ($toProcess) {
-            if (empty($assignedUserId)) {
-                if ($assignmentPermission === AclTable::LEVEL_NO && !$this->user->isApi()) {
-                    return false;
-                }
-
-                return true;
-            }
-
-            if ($assignmentPermission === AclTable::LEVEL_NO) {
-                if ($this->user->id !== $assignedUserId) {
-                    return false;
-                }
-            }
-            else if ($assignmentPermission === AclTable::LEVEL_TEAM) {
-                $teamIdList = $this->user->get('teamsIds');
-
-                if (
-                    !$this->entityManager
-                        ->getRepository('User')
-                        ->checkBelongsToAnyOfTeams($assignedUserId, $teamIdList)
-                ) {
-                    return false;
-                }
-            }
-        }
-
-        return true;
-    }
-
-    public function isPermittedTeams(Entity $entity): bool
-    {
-        $assignmentPermission = $this->acl->get('assignmentPermission');
-
-        if (
-            empty($assignmentPermission) ||
-            $assignmentPermission === true ||
-            !in_array($assignmentPermission, [AclTable::LEVEL_TEAM, AclTable::LEVEL_NO])
-        ) {
-            return true;
-        }
-
-        if (!$entity->hasLinkMultipleField('teams')) {
-            return true;
-        }
-
-        $teamIdList = $entity->getLinkMultipleIdList('teams');
-
-        if (empty($teamIdList)) {
-            if ($assignmentPermission === 'team') {
-                if ($entity->hasLinkMultipleField('assignedUsers')) {
-                    $assignedUserIdList = $entity->getLinkMultipleIdList('assignedUsers');
-
-                    if (empty($assignedUserIdList)) {
-                        return false;
-                    }
-                }
-                else if ($entity->hasAttribute('assignedUserId')) {
-                    if (!$entity->get('assignedUserId')) {
-                        return false;
-                    }
-                }
-            }
-
-            return true;
-        }
-
-        $newIdList = [];
-
-        if (!$entity->isNew()) {
-            $existingIdList = [];
-
-            $teamCollection = $this->entityManager
-                ->getRepository($entity->getEntityType())
-                ->getRelation($entity, 'teams')
-                ->select('id')
-                ->find();
-
-            foreach ($teamCollection as $team) {
-                $existingIdList[] = $team->id;
-            }
-
-            foreach ($teamIdList as $id) {
-                if (!in_array($id, $existingIdList)) {
-                    $newIdList[] = $id;
-                }
-            }
-        } else {
-            $newIdList = $teamIdList;
-        }
-
-        if (empty($newIdList)) {
-            return true;
-        }
-
-        $userTeamIdList = $this->user->getLinkMultipleIdList('teams');
-
-        foreach ($newIdList as $id) {
-            if (!in_array($id, $userTeamIdList)) {
-                return false;
-            }
-        }
-
-        return true;
+        return $this->assignmentCheckerManager->check($this->user, $entity);
     }
 
     protected function filterInputAttribute($attribute, $value)
diff --git a/application/Espo/Resources/metadata/aclDefs/Email.json b/application/Espo/Resources/metadata/aclDefs/Email.json
index a9ef77831b..8fe35a3411 100644
--- a/application/Espo/Resources/metadata/aclDefs/Email.json
+++ b/application/Espo/Resources/metadata/aclDefs/Email.json
@@ -3,5 +3,6 @@
     "ownershipCheckerClassName": "Espo\\Classes\\Acl\\Email\\OwnershipChecker",
     "portalAccessCheckerClassName": "Espo\\Classes\\AclPortal\\Email\\AccessChecker",
     "portalOwnershipCheckerClassName": "Espo\\Classes\\AclPortal\\Email\\OwnershipChecker",
+    "assignmentCheckerClassName": "Espo\\Classes\\Acl\\Email\\AssignmentChecker",
     "readOwnerUserField": "users"
 }
diff --git a/application/Espo/Resources/metadata/app/containerServices.json b/application/Espo/Resources/metadata/app/containerServices.json
index f6c2f13ef7..ce9ebf28c4 100644
--- a/application/Espo/Resources/metadata/app/containerServices.json
+++ b/application/Espo/Resources/metadata/app/containerServices.json
@@ -80,6 +80,9 @@
     "fieldValidationManager": {
         "className": "Espo\\Core\\FieldValidation\\FieldValidationManager"
     },
+    "assignmentCheckerManager": {
+        "className": "Espo\\Core\\Acl\\AssignmentChecker\\AssignmentCheckerManager"
+    },
     "hasher": {
         "className": "Espo\\Core\\Utils\\Hasher"
     },
diff --git a/application/Espo/Services/Email.php b/application/Espo/Services/Email.php
index d624be26e6..69fc29a857 100644
--- a/application/Espo/Services/Email.php
+++ b/application/Espo/Services/Email.php
@@ -963,14 +963,4 @@ class Email extends Record implements
 
         return $data;
     }
-
-    public function isPermittedAssignedUser(Entity $entity): bool
-    {
-        return true;
-    }
-
-    public function isPermittedAssignedUsers(Entity $entity): bool
-    {
-        return true;
-    }
 }
diff --git a/application/Espo/Services/Note.php b/application/Espo/Services/Note.php
index 4faa8940ac..9b3826758b 100644
--- a/application/Espo/Services/Note.php
+++ b/application/Espo/Services/Note.php
@@ -190,7 +190,7 @@ class Note extends Record
         $entity->set('post', $post);
     }
 
-    public function processAssignmentCheck(Entity $entity)
+    protected function processAssignmentCheck(Entity $entity): void
     {
         if (!$entity->isNew()) {
             return;