When you delete a message from amoCRM, the message is not deleted from the mail server. These letters will be sent to the "Deleted" folder.
Removing messages from the mail server, it will remain in amoCRM (provided that it has already been added to the system before it is deleted).
But, if the message contains an attached file, then if the message is deleted on the mail server, the file will no longer be available.
Letters in the Deleted Items folder:
are stored for 30 days
only available to Account Administrator