Bulk moving emails out of Gmail to increase space available using IMAP

Question

I would like to move in bulk thousands of emails out of Gmail into an "archive" account hosted elsewhere so that there is more room for new email.

With a "normal" IMAP account, this would be trivial. But the "Inbox" and other folders are just actually just labels in Gmail.

I can delete messages in Thunderbird from Inbox or All Mail and they get removed in Gmail Inbox and All Mail (and appear in "Trash" where I assume they will age out eventually).

But if I MOVE an email from the Inbox to a local IMAP account, the email is removed from Inbox in Gmail, but remains in "All Mail" folder, thus, not freeing up space.

If I move an email from "All Mail" to a local folder, the email seems unchanged in Gmail Inbox and All Mail.

My preference is to use current Thunderbird as the email client but I can use a special utility or maybe a plugin or whatever if it was reasonable.

In theory, I could copy/move the emails via Thunderbird and then flip over to the web interface and delete them from Gmail, but that would be extremely inefficient, especially if I was to do random selections such as by keywords or sender or whatever.

Answer 1

I recently encountered this too. I imagine that this is due to the peculiarities of how Gmail implements IMAP. See also this or the linked Bugzilla issues. I think we should consider filing a bug.

As a workaround, I've noticed that I can select a bunch of messages, choose instead to "Copy" them to a local folder, and then (since this leaves the messages selected), choosing to delete them. Gmail then understands these messages to be deleted.

In my experimentation, I noticed the following things. First, Thunderbird has a setting in "Account Settings" which lets you specify what "deleting" does with a message. Since "moving" a message seems like it should be related to "deleting" a message, it seems worth exploring the delete behavior. The Google support article suggests using the setting "Just mark it as deleted". With this setting, "deleting" a message from a "folder" corresponding to a Gmail label causes the label to be removed from the message (you might have to click the "Refresh" button on Gmail to see the updated state). "Deleting" a message from "All Mail" does not seem to have any effect. The messages are marked as deleted, but a little while later they are restored, and they are not marked as deleted on Gmail.

By contrast, the Bugzilla bugs indicate that the expected setting is "Move to this folder: [Gmail]/Trash". Using this setting and "deleting" a message from a "folder" or from "All Mail" causes the message to be marked as deleted on Gmail.

I've noticed that whatever setting I choose does seem to affect the behavior of the "Move" command. If I have chosen "Just mark as deleted", the "Move" command will mark the messages with the red strikethrough. If I have chosen "Move to this folder", the messages will disappear when moved. However, in either scenario, the behavior is the same as when the "Just mark as deleted" setting is set. Trying to "Move" a message in Thunderbird out of All Mail will hide it, but not actually remove it, and it will reappear by itself later. Trying to "Move" a message from a different folder appears to remove the label from the message. Perhaps Thunderbird's "Move" command does not mark the mails as "deleted" in the same way.