Gmail's allmail folder includes trash. Deleting the gmail trash will remove it. You can also unsubscribe from allmail in thunderbird, since it shows a duplicate of all mail.

Thanks, David.

After moving, in TB, several messages from Inbox to various Local Folders, the messages are gone from Inbox, but still exist in All Mail (message count staying at 4587, although the number Unread has dropped consistent with the files I marked as unread and then moved). There are no messages in Trash.

I've just now unsubscribed from All Mail. I then moved 32 messages to local folders (31 of which I changed to Read). Number of Unread in Inbox down by 31, total in Inbox down by 32, number of unread in All Mail unknown (folder visible only in browser, which doesn't show Unread), total in All Mail still 4587. Trash is empty.

In TB>Account Settings>Copies & Folders>Message Archives is unchecked.

In Gmail (browser)>Settings>Forwarding and POP/IMAP, I currently have Auto-Expunge off and Immediately delete the message forever. However, I've tried all these settings and have seen no change (seem to be missing the right combination).

In another account in another profile, I tried setting TB to Server Settings>Server Settings>When I delete a message: to Just mark it deleted. The two messages I then moved still appear in the Inbox in TB, with cross-out, but they're gone from my phone, but they're still in Inbox and All Mail in browser. I changed the setting back to Remove it immediately and moved one of them again to local folder, and they both then disappeared from Inbox in TB, but remained in Inbox in browser. I didn't think that would work, and boy was I right! (I deleted them from Inbox in browser and they're gone from All Mail.)

Back to the account/profile I'm setting up now, I set Gmail>Settings>...IMAP to Auto-expunge on (which makes the Archive the message (Default) the only choice) and in TB moved 16 messages. Inbox in both TB and browser down by 16. All Mail still at 4587. Trash still empty.

As I say, I can't seem to find a combination that works to delete all these messages.

Just a small addition to what david said:

A copy of every message (including those in Trash) is held in All Mail unless that message is deleted permanently. To clean out your overflowing piles of messages, delete everything you don't want, and then either Empty the Trash (there's a control for that) or select everything in the Trash folder that you don't want, and click Delete forever.

Empty the Trash and Delete forever remove those messages from All Mail.

Once you transfer messages from your IMAP boxes to your local folders, you have them permanently, but they are not completely out of the Gmail system until you delete them from All Mail and from the Trash. A shortcut method I use is this: I select all of the messages I want to move to local folders for safekeeping, then right-click on the selected block of messages and choose Copy To and follow the choices down to the folder I want to put them in. Now they're in the local folder, and while the block of messages is still selected, I click the Delete button. The last step, since I never use Trash as a storage folder for anything I really might want later, is to right-click the main Trash folder and click Empty Trash. They're gone from the Inbox, gone from the All Mail folder, and gone from the Trash. They're only present in the local folder I put them in.

It's because that All Mail folder is a confused and confusing nuisance that many users unsubscribe from it in Gmail (you can just Hide it in the Gmail Settings > labels section, and uncheck Show in Imap, and you'll not be bothered by it again).

Thanks, Wisewiz.

I've also moved messages from the Inbox to a local folder by dragging. I tried your method of Copy to, Delete. Seems like more steps/more work. HOWEVER, the 62 messages I copied/deleted are also gone from the All Mail (which now exists only on the server)!

Now the 62 messages were in Trash (but not reflected in All Mail).

So the answer might be that moving to a local folder is not seen as deleting from the server.

Also, I tried changing the Server Settings>Server Settings>When I delete a message, which was = Move to this folder>Trash on [server], to = Remove it immediately. Then I tried another Copy to/Delete. No change in All Mail, no messages in Trash.

I changed the setting back and did another 3 sets of Copy to/Delete. One time worked as above (All Mail reduced and messages in Trash, but the other 2 sets there was no change in All Mail, nothing in Trash.

So my takeaway is your phrase, "All Mail folder is a confused and confusing nuisance".

Sez you: "So the answer might be that moving to a local folder is not seen as deleting from the server."

Perzactly! What you have accomplished, however, is you've taken your copies of those messages out of the control of the server. Then the task remains to take the load off the server by doing some housekeeping.

When you move copies to your own local folders, you are not deleting them and then emptying the Trash, you are just copying them. The fact that they disappear from an IMAP folder in TB doesn't mean they're deleted. In order to remove anything from the server (AND thus from All Mail), you've gotta delete that message and then clear it from the trash.

I actually find housekeeping easier in the server online interface than in TBird. I can check the server's folders/labels, select the unwanted stuff, send it to the Trash folder, and then open the Trash and either delete all, or do some picking and choosing and delete the rest. Sometimes, I just click the box at the top of the column to select ALL, and then go down the column and UNcheck any individual things I might want to give another think to.

Then when you re-open TBird (did I mention that it's a good idea to close TBird before you open the online interface and start housekeeping?), you'll see the syncing happening with each folder you open (the spinner is the evidence), and you'll see the results of your work online.

I see no reason to have the server stuck with long-term care of my messages. I put 'em in my local folders and take 'em off the server, and image my OS and program drives every night (only takes a minute and a half or so) so that if disaster were ever to strike, I have all my important stuff backed up and can recover in a flash.

"I see no reason to have the server stuck with long-term care of my messages."

Right, that and I want to control my own security (incl whatever Google might be doing). In fact, that's the main reason this All Mail thing has been bothering me.

So anyway, by Copy to/Delete, I was able to take several hundred messages off the server, incl out of All Mail. Then I looked at my online folders, found the oldest dates (about two years old in this account), then use the "Oldest" sort function in the browser and start deleting everything until I got close to the actually-existing messages (dumped about 2000 messages up to seven years old!).

I'll have to pick carefully from now on, but I only 954 left.

Thanks, David and Wisewiz

You're entirely welcome. And that was a wise move on your part. Keeping the number of items stored on a distant and uncontrollable (by us, I mean) server to a reasonable number, and keeping things of serious value OFF the server and on our hard drives AND backed up -- that's a thinking person's way to go.