diff --git a/application/Espo/Core/Mail/Account/GroupAccount/Hooks/BeforeFetch.php b/application/Espo/Core/Mail/Account/GroupAccount/Hooks/BeforeFetch.php
index a21a00a6e7..3217530129 100644
--- a/application/Espo/Core/Mail/Account/GroupAccount/Hooks/BeforeFetch.php
+++ b/application/Espo/Core/Mail/Account/GroupAccount/Hooks/BeforeFetch.php
@@ -68,7 +68,7 @@ class BeforeFetch implements BeforeFetchInterface
     {
         if (
             $message->hasHeader('from') &&
-            preg_match('/MAILER-DAEMON|POSTMASTER/i', $message->getHeader('from'))
+            preg_match('/MAILER-DAEMON|POSTMASTER/i', $message->getHeader('from') ?? '')
         ) {
             try {
                 $toSkip = $this->processBounced($message);
@@ -113,7 +113,7 @@ class BeforeFetch implements BeforeFetchInterface
         else {
             $to = $message->getHeader('to');
 
-            if (preg_match('/\+bounce-qid-[a-z0-9\-]*/', $to, $m)) {
+            if (preg_match('/\+bounce-qid-[a-z0-9\-]*/', $to ?? '', $m)) {
                 /** @var array{string} */
                 $arr = preg_split('/\+bounce-qid-/', $m[0], -1, \PREG_SPLIT_NO_EMPTY);
 
diff --git a/application/Espo/Core/Mail/Account/GroupAccount/Service.php b/application/Espo/Core/Mail/Account/GroupAccount/Service.php
index 08410abd3b..f05629a6e1 100644
--- a/application/Espo/Core/Mail/Account/GroupAccount/Service.php
+++ b/application/Espo/Core/Mail/Account/GroupAccount/Service.php
@@ -81,7 +81,8 @@ class Service
 
             $params = $params
                 ->withPassword(
-                    $params->getPassword() ?? $this->crypt->decrypt($account->getPassword())
+                    $params->getPassword() ??
+                    $this->crypt->decrypt($account->getPassword() ?? '')
                 )
                 ->withImapHandlerClassName($account->getImapHandlerClassName());
         }
@@ -98,7 +99,8 @@ class Service
 
             $params = $params
                 ->withPassword(
-                    $params->getPassword() ?? $this->crypt->decrypt($account->getPassword())
+                    $params->getPassword() ??
+                    $this->crypt->decrypt($account->getPassword() ?? '')
                 )
                 ->withImapHandlerClassName($account->getImapHandlerClassName());
         }
diff --git a/application/Espo/Core/Mail/Account/GroupAccount/StorageFactory.php b/application/Espo/Core/Mail/Account/GroupAccount/StorageFactory.php
index ff788e08a8..292e274a39 100644
--- a/application/Espo/Core/Mail/Account/GroupAccount/StorageFactory.php
+++ b/application/Espo/Core/Mail/Account/GroupAccount/StorageFactory.php
@@ -64,7 +64,7 @@ class StorageFactory implements StorageFactoryInterface
             ->setSecurity($account->getSecurity())
             ->setUsername($account->getUsername())
             ->setPassword(
-                $this->crypt->decrypt($account->getPassword())
+                $this->crypt->decrypt($account->getPassword() ?? '')
             )
             ->setId($account->getId())
             ->setImapHandlerClassName($account->getImapHandlerClassName())
@@ -104,7 +104,7 @@ class StorageFactory implements StorageFactoryInterface
                 );
             }
 
-            if (method_exists($handler, 'prepareProtocol')) {
+            if ($handler && method_exists($handler, 'prepareProtocol')) {
                 // for backward compatibility
                 $rawParams['ssl'] = $rawParams['security'] ?? null;
 
diff --git a/application/Espo/Core/Mail/Account/PersonalAccount/Account.php b/application/Espo/Core/Mail/Account/PersonalAccount/Account.php
index a3fb0ee578..d4ac03c29a 100644
--- a/application/Espo/Core/Mail/Account/PersonalAccount/Account.php
+++ b/application/Espo/Core/Mail/Account/PersonalAccount/Account.php
@@ -68,11 +68,15 @@ class Account implements AccountInterface
             throw new Error("No assigned user.");
         }
 
-        $this->user = $this->entityManager->getEntity(User::ENTITY_TYPE, $this->entity->getAssignedUser()->getId());
+        $userId = $this->entity->getAssignedUser()->getId();
 
-        if (!$this->user) {
+        $user = $this->entityManager->getEntityById(User::ENTITY_TYPE, $userId);
+
+        if (!$user) {
             throw new Error("Assigned user not found.");
         }
+
+        $this->user = $user;
     }
 
     public function updateFetchData(FetchData $fetchData): void
@@ -114,10 +118,12 @@ class Account implements AccountInterface
     {
         $linkMultiple = LinkMultiple::create();
 
+        $userLink = $this->getUser();
+
         return $linkMultiple->withAdded(
             LinkMultipleItem
-                ::create($this->getUser()->getId())
-                ->withName($this->getUser()->getName())
+                ::create($userLink->getId())
+                ->withName($userLink->getName() ?? '')
         );
     }
 
@@ -128,7 +134,13 @@ class Account implements AccountInterface
 
     public function getUser(): Link
     {
-        return $this->entity->getAssignedUser();
+        $userLink = $this->entity->getAssignedUser();
+
+        if (!$userLink) {
+            throw new Error("No assigned user.");
+        }
+
+        return $userLink;
     }
 
     public function getTeams(): LinkMultiple
@@ -144,7 +156,7 @@ class Account implements AccountInterface
         return $linkMultiple->withAdded(
             LinkMultipleItem
                 ::create($team->getId())
-                ->withName($team->getName())
+                ->withName($team->getName() ?? '')
         );
     }
 
diff --git a/application/Espo/Core/Mail/Account/PersonalAccount/Service.php b/application/Espo/Core/Mail/Account/PersonalAccount/Service.php
index cb3d6b3ced..c1e5036f93 100644
--- a/application/Espo/Core/Mail/Account/PersonalAccount/Service.php
+++ b/application/Espo/Core/Mail/Account/PersonalAccount/Service.php
@@ -98,7 +98,8 @@ class Service
 
             $params = $params
                 ->withPassword(
-                    $params->getPassword() ?? $this->crypt->decrypt($account->getPassword())
+                    $params->getPassword() ??
+                    $this->crypt->decrypt($account->getPassword() ?? '')
                 )
                 ->withImapHandlerClassName($account->getImapHandlerClassName());
         }
@@ -136,7 +137,8 @@ class Service
 
             $params = $params
                 ->withPassword(
-                    $params->getPassword() ?? $this->crypt->decrypt($account->getPassword())
+                    $params->getPassword() ??
+                    $this->crypt->decrypt($account->getPassword() ?? '')
                 )
                 ->withImapHandlerClassName($account->getImapHandlerClassName());
         }
diff --git a/application/Espo/Core/Mail/Account/PersonalAccount/StorageFactory.php b/application/Espo/Core/Mail/Account/PersonalAccount/StorageFactory.php
index dc67013e98..41f2788305 100644
--- a/application/Espo/Core/Mail/Account/PersonalAccount/StorageFactory.php
+++ b/application/Espo/Core/Mail/Account/PersonalAccount/StorageFactory.php
@@ -45,6 +45,7 @@ use Espo\Repositories\UserData as UserDataRepository;
 
 use Espo\ORM\EntityManager;
 
+use LogicException;
 use Throwable;
 
 class StorageFactory implements StorageFactoryInterface
@@ -71,16 +72,24 @@ class StorageFactory implements StorageFactoryInterface
 
     public function create(Account $account): LaminasStorage
     {
+        $userLink = $account->getUser();
+
+        if (!$userLink) {
+            throw new LogicException("No user for mail account.");
+        }
+
+        $userId = $userLink->getId();
+
         $params = Params::createBuilder()
             ->setHost($account->getHost())
             ->setPort($account->getPort())
             ->setSecurity($account->getSecurity())
             ->setUsername($account->getUsername())
             ->setPassword(
-                $this->crypt->decrypt($account->getPassword())
+                $this->crypt->decrypt($account->getPassword() ?? '')
             )
             ->setEmailAddress($account->getEmailAddress())
-            ->setUserId($account->getUser()->getId())
+            ->setUserId($userId)
             ->setId($account->getId())
             ->setImapHandlerClassName($account->getImapHandlerClassName())
             ->build();
@@ -123,7 +132,7 @@ class StorageFactory implements StorageFactoryInterface
                 );
             }
 
-            if (method_exists($handler, 'prepareProtocol')) {
+            if ($handler && method_exists($handler, 'prepareProtocol')) {
                 // for backward compatibility
                 $rawParams['ssl'] = $rawParams['security'] ?? null;
 
@@ -140,7 +149,7 @@ class StorageFactory implements StorageFactoryInterface
                 $imapHandlers = $userData->get('imapHandlers') ?? (object) [];
 
                 if (isset($imapHandlers->$emailAddress)) {
-                    /** @var ?class-string */
+                    /** @var class-string */
                     $handlerClassName = $imapHandlers->$emailAddress;
 
                     try {
@@ -153,7 +162,7 @@ class StorageFactory implements StorageFactoryInterface
                         );
                     }
 
-                    if (method_exists($handler, 'prepareProtocol')) {
+                    if ($handler && method_exists($handler, 'prepareProtocol')) {
                         $imapParams = $handler->prepareProtocol($userId, $emailAddress, $rawParams);
                     }
                 }
diff --git a/application/Espo/Core/Mail/FiltersMatcher.php b/application/Espo/Core/Mail/FiltersMatcher.php
index 4c7dd75165..8d5fb95aee 100644
--- a/application/Espo/Core/Mail/FiltersMatcher.php
+++ b/application/Espo/Core/Mail/FiltersMatcher.php
@@ -49,13 +49,16 @@ class FiltersMatcher
         foreach ($filterList as $filter) {
             $filterCount = 0;
 
-            if ($filter->getFrom()) {
+            $from = $filter->getFrom();
+            $subject = $filter->getSubject();
+
+            if ($from) {
                 $filterCount++;
 
                 if (
                     !$this->matchString(
-                        strtolower($filter->getFrom()),
-                        strtolower($email->getFromAddress())
+                        strtolower($from),
+                        strtolower($email->getFromAddress() ?? '')
                     )
                 ) {
                     continue;
@@ -70,10 +73,12 @@ class FiltersMatcher
                 }
             }
 
-            if ($filter->getSubject()) {
+            if ($subject) {
                 $filterCount++;
 
-                if (!$this->matchString($filter->getSubject(), $email->getSubject())) {
+                if (
+                    !$this->matchString($subject, $email->getSubject() ?? '')
+                ) {
                     continue;
                 }
             }
@@ -100,9 +105,20 @@ class FiltersMatcher
 
     private function matchTo(Email $email, EmailFilter $filter): bool
     {
+        $filterTo = $filter->getTo();
+
+        if ($filterTo === null) {
+            return false;
+        }
+
         if (count($email->getToAddressList())) {
             foreach ($email->getToAddressList() as $to) {
-                if ($this->matchString(strtolower($filter->getTo()), strtolower($to))) {
+                if (
+                    $this->matchString(
+                        strtolower($filterTo),
+                        strtolower($to)
+                    )
+                ) {
                     return true;
                 }
             }
@@ -122,11 +138,11 @@ class FiltersMatcher
                 continue;
             }
 
-            if (stripos($bodyPlain, $phrase) !== false) {
+            if ($bodyPlain && stripos($bodyPlain, $phrase) !== false) {
                 return true;
             }
 
-            if (stripos($body, $phrase) !== false) {
+            if ($body && stripos($body, $phrase) !== false) {
                 return true;
             }
         }
diff --git a/application/Espo/Core/Mail/Importer.php b/application/Espo/Core/Mail/Importer.php
index 60cd843711..5fd74080b5 100644
--- a/application/Espo/Core/Mail/Importer.php
+++ b/application/Espo/Core/Mail/Importer.php
@@ -34,6 +34,8 @@ use Espo\Repositories\Email as EmailRepository;
 
 use Espo\ORM\EntityManager;
 
+use Espo\Core\Utils\DateTime as DateTimeUtil;
+
 use Espo\Core\Notification\AssignmentNotificator;
 use Espo\Core\Notification\AssignmentNotificatorFactory;
 use Espo\Core\Notification\AssignmentNotificator\Params as AssignmentNotificatorParams;
@@ -182,6 +184,7 @@ class Importer
             $parser->hasHeader($message, 'message-Id') &&
             $parser->getHeader($message, 'message-Id')
         ) {
+            /** @var string */
             $messageId = $parser->getMessageId($message);
 
             $email->set('messageId', $messageId);
@@ -217,25 +220,35 @@ class Importer
 
         if ($parser->hasHeader($message, 'date')) {
             try {
-                $dt = new DateTime($parser->getHeader($message, 'date'));
+                /** @var string */
+                $dateHeaderValue = $parser->getHeader($message, 'date');
 
-                $dateSent = $dt->setTimezone(new DateTimeZone('UTC'))->format('Y-m-d H:i:s');
+                $dt = new DateTime($dateHeaderValue);
+
+                $dateSent = $dt
+                    ->setTimezone(new DateTimeZone('UTC'))
+                    ->format(DateTimeUtil::SYSTEM_DATE_TIME_FORMAT);
 
                 $email->set('dateSent', $dateSent);
             }
             catch (Exception $e) {}
         }
         else {
-            $email->set('dateSent', date('Y-m-d H:i:s'));
+            $email->set('dateSent', date(DateTimeUtil::SYSTEM_DATE_TIME_FORMAT));
         }
 
         if ($parser->hasHeader($message, 'delivery-Date')) {
             try {
-                $dt = new DateTime($parser->getHeader($message, 'delivery-Date'));
+                /** @var string */
+                $deliveryDateHeaderValue = $parser->getHeader($message, 'delivery-Date');
 
-                $deliveryDate = $dt->setTimezone(new DateTimeZone('UTC'))->format('Y-m-d H:i:s');
+                $dt = new DateTime($deliveryDateHeaderValue);
 
-                $email->set('delivery-Date', $deliveryDate);
+                $deliveryDate = $dt
+                    ->setTimezone(new DateTimeZone('UTC'))
+                    ->format(DateTimeUtil::SYSTEM_DATE_TIME_FORMAT);
+
+                $email->set('deliveryDate', $deliveryDate);
             }
             catch (Exception $e) {}
         }
@@ -280,6 +293,7 @@ class Importer
                 if ($replied) {
                     $email->set('repliedId', $replied->getId());
 
+                    /** @var string[] */
                     $repliedTeamIdList = $replied->getLinkMultipleIdList('teams');
 
                     foreach ($repliedTeamIdList as $repliedTeamId) {
@@ -449,6 +463,7 @@ class Importer
             return;
         }
 
+        /** @var string[] */
         $parentTeamIdList = $parent->getLinkMultipleIdList('teams');
 
         foreach ($parentTeamIdList as $parentTeamId) {
@@ -653,6 +668,7 @@ class Importer
 
         $duplicate->loadLinkMultipleField('users');
 
+        /** @var string[] */
         $fetchedUserIdList = $duplicate->getLinkMultipleIdList('users');
 
         $duplicate->setLinkMultipleIdList('users', []);
@@ -710,6 +726,7 @@ class Importer
             );
         }
 
+        /** @var string[] */
         $fetchedTeamIdList = $duplicate->getLinkMultipleIdList('teams');
 
         foreach ($teamIdList as $teamId) {
@@ -731,9 +748,9 @@ class Importer
 
             $dt->modify('+5 seconds');
 
-            $executeAt = $dt->format('Y-m-d H:i:s');
+            $executeAt = $dt->format(DateTimeUtil::SYSTEM_DATE_TIME_FORMAT);
 
-            $job = $this->entityManager->getEntity('Job');
+            $job = $this->entityManager->getNewEntity('Job');
 
             $job->set([
                 'serviceName' => 'Stream',
diff --git a/application/Espo/Core/Mail/Mail/Header/XQueueItemId.php b/application/Espo/Core/Mail/Mail/Header/XQueueItemId.php
index bbe2b55863..4d6337db02 100644
--- a/application/Espo/Core/Mail/Mail/Header/XQueueItemId.php
+++ b/application/Espo/Core/Mail/Mail/Header/XQueueItemId.php
@@ -44,7 +44,7 @@ class XQueueItemId implements Header\HeaderInterface
     private ?string $id = null;
 
     /**
-     * @param ?string $headerLine
+     * @param string $headerLine
      * @return self
      */
     public static function fromString($headerLine)
diff --git a/application/Espo/Core/Mail/Mail/Storage/Imap.php b/application/Espo/Core/Mail/Mail/Storage/Imap.php
index 94b01e56e6..2dd04d59fd 100644
--- a/application/Espo/Core/Mail/Mail/Storage/Imap.php
+++ b/application/Espo/Core/Mail/Mail/Storage/Imap.php
@@ -38,6 +38,8 @@ class Imap extends \Laminas\Mail\Storage\Imap
     {
         $nextUid = strval(intval($uid) + 1);
 
+        assert($this->protocol !== null);
+
         return $this->protocol->search(['UID ' . $nextUid . ':*']);
     }
 
@@ -46,6 +48,8 @@ class Imap extends \Laminas\Mail\Storage\Imap
      */
     public function getIdsSinceDate(string $date): array
     {
+        assert($this->protocol !== null);
+
         return $this->protocol->search(['SINCE "' . $date . '"']);
     }
 
@@ -55,6 +59,8 @@ class Imap extends \Laminas\Mail\Storage\Imap
      */
     public function getHeaderAndFlags(int $id): array
     {
+        assert($this->protocol !== null);
+
         /** @var array{'RFC822.HEADER': string, FLAGS: string[]} */
         $data = $this->protocol->fetch(['FLAGS', 'RFC822.HEADER'], $id);
 
diff --git a/application/Espo/Core/Mail/MessageWrapper.php b/application/Espo/Core/Mail/MessageWrapper.php
index c5f9e48f6d..98439aadb9 100644
--- a/application/Espo/Core/Mail/MessageWrapper.php
+++ b/application/Espo/Core/Mail/MessageWrapper.php
@@ -31,6 +31,8 @@ namespace Espo\Core\Mail;
 
 use Espo\Core\Mail\Account\Storage;
 
+use RuntimeException;
+
 class MessageWrapper implements Message
 {
     private int $id;
@@ -81,17 +83,29 @@ class MessageWrapper implements Message
 
     public function hasHeader(string $name): bool
     {
-        return $this->getParser()->hasHeader($this, $name);
+        if (!$this->parser) {
+            throw new RuntimeException();
+        }
+
+        return $this->parser->hasHeader($this, $name);
     }
 
     public function getHeader(string $attribute): ?string
     {
-        return $this->getParser()->getHeader($this, $attribute);
+        if (!$this->parser) {
+            throw new RuntimeException();
+        }
+
+        return $this->parser->getHeader($this, $attribute);
     }
 
     public function getRawContent(): string
     {
         if (is_null($this->rawContent)) {
+            if (!$this->storage) {
+                throw new RuntimeException();
+            }
+
             $this->rawContent = $this->storage->getRawContent($this->id);
         }
 
diff --git a/application/Espo/Core/Mail/Sender.php b/application/Espo/Core/Mail/Sender.php
index e7d1d475df..b347759777 100644
--- a/application/Espo/Core/Mail/Sender.php
+++ b/application/Espo/Core/Mail/Sender.php
@@ -602,7 +602,9 @@ class Sender
 
         $htmlPart = null;
 
-        if ($email->get('isHtml')) {
+        $isHtml = $email->get('isHtml');
+
+        if ($isHtml) {
             $htmlPart = new MimePart($email->getBodyForSending());
 
             $htmlPart->encoding = Mime::ENCODING_QUOTEDPRINTABLE;
@@ -613,7 +615,7 @@ class Sender
         if (!empty($attachmentPartList)) {
             $messageType = 'multipart/related';
 
-            if ($email->get('isHtml')) {
+            if ($isHtml) {
                 $content = new MimeMessage();
 
                 $content->addPart($textPart);
@@ -637,7 +639,7 @@ class Sender
             }
         }
         else {
-            if ($email->get('isHtml')) {
+            if ($isHtml) {
                 $body->setParts([$textPart, $htmlPart]);
 
                 $messageType = 'multipart/alternative';
@@ -698,6 +700,8 @@ class Sender
 
             $message->getHeaders()->addHeader($messageIdHeader);
 
+            assert($this->transport !== null);
+
             $this->transport->send($message);
 
             $email->set('status', 'Sent');