This question is similar to that referenced in archived question thread https://support.mozilla.org/en-US/questions/1206188 I've been having this problem too following upgrades to TBird. TBird has always been very reliable for me, so I didn't notice at first that several of the outgoing SMTP servers associated with each email account had been reset to an alternate seemingly at random. Despite using the recommended solution in the above thread, I am not able to reset my outgoing SMTP server user name to the correct email address. After resetting the user name in the SMTP server window, upon verification the user name reverts, often to the user name of the previous alternate email account I attempted to reset. In other words, when I change the outgoing SMTP server user name for one alternate account, changes to another account are undone. The problem occurs with some alternates but not others. All accounts are Gmail IMAP. TBird version is 78.9.0. Just upgraded to 78.12.0 and problem persists.