Comment 54 for bug 13983

Again, as you noted - there are clients doing that, so this is not a technical limitation of the IMAP protocol. I admit I have not studied the RFC for IMAP, perhaps it says that the only accepted way to delete mail is to mark them as deleted instead of moving it to the Trash folder.

Be it this way or the other - please do not think of "technical arguments" as something old-fashioned or something that stands in the way of progress. What we need are well-designed and well-defined standards that would boost the progress. Now imagine how would modern email access look like if there was no IMAP nor POP and all the email providers created their own "user-friendly" protocol for doing that.