Users may find they cannot remove files or attachments from records linked to Email Message objects, including those created via Email-to-Case. This limitation is caused by special access rules on the EmailMessage object that restrict edit and remove operations for most users.
To Edit File Details in Lightning Experience, users must be the file owner, a collaborator, or have the "Modify All Data" permission. When files are associated with an EmailMessage record, these requirements become more restrictive.
Two org configurations can affect this behavior:
The EmailMessage object has special access rules that limit who can edit or remove associated files. The resolution depends on which org configuration applies to your situation.
Users need at least Read and Edit access to all of the file's related records, or must be set as a Collaborator in the file's sharing settings, in order to Remove a File from a Record. An Admin or file owner can Share Files with People in Lightning Experience and set the desired users as Collaborators.
When Enhanced Email is active and attachments are saved as Salesforce Files, only the following users can remove files related to email-to-case records:
To allow other users to remove these files, an Admin or the file owner must share the file and grant Collaborator access to the desired users.
Edit File Details in Lightning Experience
Share Files with People in Lightning Experience
EmailMessage Object Documentation
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