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.