reply all replies to all of the addresses in the current email. So open the email in a tab and look at the addresses listed in the header. If it is only yours, then reply all will only reply to you. You are the only recipient of the current email. Addresses in To and CC will be included but obviously not BCC recipient's as their information is simply not included in the email. The only BCC recipient that will ever be included is mail from your own sent items.

Reply all does not, never has, and I would expect never, will look back through the conversation, identify all the unique addresses used, over what could be a period of years, and reply to them all. As for the smart reply, I use buttons on the main toolbar and an add-on to reduce the header to one line, so I really have not seen it in years. I can not abide the wasted space the email header occupies when reading in the reading pane.

I wasn't clear. REPLY ALL should work, but that command is NOT AVAILABLE.

Email 1 was other person to me. Email 2 was my reply to other person (using REPLY). If I go in the sent file, open email 2 (which was addressed the other person as it was replying to email 1) and hit REPLY, TB replies to ME (last author) rather than to the other person (last recipient).

The only option TB gives me in this situation is REPLY, and in a sent email it's picking the wrong person to reply to.

You wrote that Sent message. It seems a perfectly logical reaction for Reply to reply to whoever sent it i.e. you. It sounds as if you want it to understand the particular context of it sitting in your Sent folder and then do something different.

I file my sent messages into topic-related folders alongside incoming and other outgoing messages. So there is no context to help work out when to treat a message differently. And say I'd Cc'd myself on another account. Is it supposed to recognize, in all situations, when an addressee is one or other of my own addresses?

Use Edit As New if you want to re-use a message.

And like Matt, I abhor that wasteful central toolbar, putting my mfu controls on the main toolbar. I use a right-click when I need something I can't see a button for. And hey, look, there is Reply All.

My problem isn't with REPLY (which I can understand going to me). It's the LACK of a REPLY ALL option, so I can't send it to the other person as well. The only way to get it to them is to forward it, and re-enter their address.

While you may abhor the central toolbar, adding a REPLY ALL button (even if only to the MORE dropdown), doesn't use any additional screen height.

I simply want a REPLY ALL option for SENT emails, so that ALL the addressees on the sent email can get an email.

Right click the main toolbar at the top of the windows. Select customize. Add the reply all button to your main toolbar.