I'm guessing here because you have not supplied much information. What OS are you using ? What version of Thunderbird are you using? 'All Mail' is a folder on a gmail server - Are you talking about a Gmail Imap account? I'll presume you are talking about a gmail imap account. Gmail stores all emails, incoming and outgoing in the 'All MAil' folder. All emails you see in Inbox, Sent and all other imap gmail folders will also be in the 'All Mail'. If you delete anything in the 'All Mail' folder, it will be delete off server and will also be deleted from any other folder it appears in. I would advise anyone, that it may be safer to not subscribe to see the 'All Mail' folder as misuse or folder corruption may lead to dataloss. Recently, the developers had a brainwave and though it would be a really neat idea to rename all default server folders to use a set naming convention regardless of what each server actually uses. This has caused some issues and a lot of confusion. eg: the 'All Mail' folder got auto renamed to say 'Archives' In reality the folder is still the 'All Mail' folder but it just displays as 'Archives'. The 'All Mail' folder is not just an archive - it is everything. There are bug reports already trying to get this sorted asap. You can follow this one if you like: https://bugzilla.mozilla.org/show_bug.cgi?id=2001557