If you are having problems with Thunderbird and IMAP connections, specifically hang-ups while listing large email folder contents then we suggest the following thunderbird advanced config change.
Under the menu: Tools / Options / Advanced tab / Config Editor do a search for either of the following settings
mail.imap.fetch_by_chunks OR mail.server.default.fetch_by_chunks (Depends on thunderbird version) and set them to false (default is true)
Close and restart your email client.
Your IMAP experience should now be much improved.
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