I'm trying to better understand how Thunderbird communicates that messages are deleted to the servers of the respective email accounts configured as IMAP. Specifically, it seems that when moving a message from an IMAP folder, such as an Inbox, to a folder of a different email account or a Local Folder, the message disappears from Thunderbird but doesn't immediately get deleted from the server (I am checking by logging in through a browser to the email's web interface). Depending on the email provider, it may be marked or flagged as "deleted" or in some cases it just remains in the inbox (in outlook's web interface, for example, I can't tell if a message has been marked as deleted or not). Only later, after right-clicking on the respective inbox in Thunderbird and choosing "Compact" it deletes the message from the server. I'm a bit confused now: All of my accounts are using maildir (https://support.mozilla.org/en-US/kb/maildir-thunderbird) as storage format, which I selected prior to adding any account. According to the information here (https://support.mozilla.org/en-US/kb/compacting-folders), "Compact does not apply to accounts using the maildir storage format". So for maildir accounts, why do I have a "compact" option at all and how come it doesn't delete messages immediately? Or perhaps I'm misunderstanding either what compact means or maildir or (probably) both? Is there a way to have Thunderbird simply delete (not just "mark as deleted") moved messages instantly? I was under the impression that since maildir stores essentially one file per email message, that it would function like file management on a computer, so when moving a message from folder A to folder B the file/message would disappear from folder A, not that it would keep a copy "marked as deleted" in folder A. If anybody could explain this I would be most grateful.