I have two Gmail accounts that I use to manage the band I'm in. Let's call them 'venues@gmail.com' and 'punters@gmail.com'. I access both accounts using Thunderbird 115.13.0 (64-bit), under Linux Mint. When someone emails the band on the Punters address I reply to it in Thunderbird, which automatically sets my From: address as punters@gmail.com. What happens next is that my reply appears in the Sent Items for BOTH Punters and Venues. The copy in the Punters sent folder says that it's from "Punters <punters@gmail.com>", but the copy in the Venues sent folder says it's from "Punters <venues@gmail.com>". When I examine the headers, there's extra stuff in the copy in the Venues account, specifically a 'Received: from' entry that makes it look like the email has been routed via a Google server, so suspect this might be a Google issue and not a Thunderbird one, but I'm not sure. The email headers for the two copies include the following lines: Punters copy: From: Punters <punters@gmail.com> Reply-To: punters@gmail.com Venues copy: From: Punters <venues@gmail.com> Reply-To: punters@gmail.com X-Google-Original-From: Punters <punters@gmail.com> The problem I have is that when people reply back to my reply, while most often they're sent to punters@gmail.com, sometimes they're sent to venues@gmail.com. That is, some email clients appear to be sending to what's in the 'From:' field, not the 'Reply-To:' field (or the X-Google-Original-From one). The Venues address is only used by me, where the Punters address is shared with two other band members, so it matters what email address people reply to. I've examined the account settings for both email addresses in Thunderbird and in Google, and can't work out what's going on. I've been using this email setup for the last decade. I'm not sure when this started happening, but possibly only within the last 6 months or so. Has anyone seen this behaviour before and know how to stop it?