This one has been vexing me literally for years, but I finally figured it out, I think. At least, I can repeat the issue. The symptom: sometimes when picking reply or reply-all, thunderbird puts in somebody else's from address from my organization! Version 102.10.0 (64-bit) and earlier! (at least 2 years) Setup: I have 2 accounts setup, a work account and a personal. The work account is the second one in the setup order (this may be significant, or not) When I get an email to my work account, I want the reply address when I click on the reply or reply-all button to come from this account. So, I check the checkbox under account settings that says " Reply from this identify when delivery headers match: and I put in the work *@domain.com address But, if I use *@domain.com, in certain emails, when I click reply or reply-all, it uses somebody else's address, sometimes (not always). If I use just domain.com without the *@, it doesn't do this. When this is combined with an email header that has a line matching: X-Google-Original-From: <someaddress> - it will use this address!! If I just use domain.com, it doesn't do this. If the message that I'm replying to doesn't have this header, it uses my correct from address (I have not exhaustively tested this part, but it appears to be true in a sample test of about 5 messages with and without this header) The combination of these 2 things seems to expose a devilish bug! I hope this helps to resolve this issue that I have seen bug reports about, seemingly back to 2014.