I've seen this issue raised in a number of posts but it just seems to be an error. If I'm reading an email and click Reply, the From should be the address the email came to. It isn't. Yes, there are cases of ambiguity, like if the original came to multiple of my addresses, but that's not the case. This isn't a gmail account (I've seen some issues around those.) It is set to the right reply address (that setting is empty) and uses the right SMTP server. I don't want all my mail coming to Local Folders and don't want the Unified view. I have a folder for me@mydomain.com. I've added another address, also-me@mydomain.com. I want those emails to come into the same folder as me@mydomain.com. That works fine. But if it came to also-me@ and I hit reply then the From should be also-me@. It's not. It's me@. I see there's an add-on that can help. This shouldn't need an add-on, it's an error. That add-on conflicts with Identity Chooser which is very useful so that's not a solution. I just can't imagine (barring a case of ambiguity) what logic would lead to the From being anything but the address the original came to. It's just plain an error.