My email host supports both POP3 and IMAP retrieval, and for years, I've been using POP3 in Thunderbird to retrieve my email. I'd like to switch to IMAP so that messages can be easily stored on the server and automatically backed up by my email host.

If I switch Thunderbird from POP3 to IMAP mode for that account, what happens to the messages currently in my inbox and other folders in Thunderbird? Will TB try to upload them to the server, or delete them because they're not on the server, or something else odd? Or will they simply remain on the client without being on the server, and only new mail will be synchronized with the server?

Thanks for your help.

1 Answer 1


You cannot switch account types in Thunderbird – you can only create a new IMAP account and remove the old one.

Messages fetched from POP3 will remain stored in "Local Folders", even after the account is deleted. The IMAP account will instead show up as a completely separate folder tree, with its own (server-side) inbox and folders.

In other words, Thunderbird will see two completely separate accounts, and will not attempt to do anything with your previously fetched mail. You'll be able to copy it to the IMAP server manually, though.

  • Probably worth noting that for large accounts, the second IMAP copy could take a long time to sync and eat up lots of disk space if the OP wants to sync everything (which it sounds like the OP desires since they mention having a backup)
    – ernie
    Commented Mar 18, 2013 at 16:22
  • @ernie: POP clients delete fetched mail from servers by default, so the IMAP inbox is probably empty now. Commented Mar 18, 2013 at 16:39

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