SETUP: I check multiple gmail accounts from Thunderbird via IMAP: [email protected] [email protected] [email protected] I also have a couple forwarding setups: [email protected] -> [email protected] (this domain is managed by google and google does the forwarding) [email protected] -> [email protected] (I set this to forward through the gmail web interface; I don't check this old address directly) I try to keep my setup simple. I don't do any folder sorting; I just keep messages in "inbox" until I archive it. I don't have any plugins. I don't have any identities other than what is made with each account. I am updated to the latest TB version, 102.12.0 (64-bit). PROBLEM: #1: I send an email from [email protected] to [email protected]. The message eventually arrives in the inbox of [email protected]. When I reply to this message (reply or reply all), a compose window opens with: From = [email protected] To = [email protected] These should be: From = [email protected] To = [email protected] I get the expected behavior when: I send from someone else's account [email protected] to my [email protected]. I send from [email protected] to [email protected]. (This result is important.) #2: I get a similar problem when I send an email from [email protected] to [email protected]. I eventually get the message at [email protected]. When I click reply, the compose window shows: From = [email protected] To = [email protected] These should be: From = [email protected] To = [email protected] DISCUSSION: It seems that when a message is forwarded to another address AND Thunderbird has BOTH the originator account and the recipient account, a reply to that message picks up the wrong FROM and TO fields. When testing this setup, I initially thought the problem was more widespread affecting external accounts too but now I see that it is only if the same instance of TB has both accounts. I suppose as it is, this isn't a big problem as I don't actually send messages to myself. I only did this for testing and it confused me for a while. I have seen a couple other posts mention this problem. The suggested solution is to configure identities but this /has/ to be a bug that should be resolved. It doesn't make sense that it would work like this. RELATED: Errors populating To, From, and Reply-To fields on replies https://support.mozilla.org/en-US/questions/1239772 How can I reply to the sender instead of replying to my alias I got the email from? https://support.mozilla.org/en-US/questions/1370144