espocrm-base/application/Espo/Modules/Crm/Resources/metadata/selectDefs/EmailQueueItem.json

{
    "primaryFilterClassNameMap": {
        "pending": "Espo\\Modules\\Crm\\Classes\\Select\\EmailQueueItem\\PrimaryFilters\\Pending",
        "failed": "Espo\\Modules\\Crm\\Classes\\Select\\EmailQueueItem\\PrimaryFilters\\Failed",
        "sent": "Espo\\Modules\\Crm\\Classes\\Select\\EmailQueueItem\\PrimaryFilters\\Sent"
    }
}