[tomcatfish]

Thunderbird will allow you to "Customize From address", where you type something into the "From" field and it attempts to send the message using your normal log in credentials. Works like a charm for me on Ubuntu, and I imagine it is available with the same features on Mac.

[pm7]

I recommend checking out add-on Virtual Identity for Thunderbird. It will use "To" address as "From" by default when writing reply, allows editing "From" directly in new mails and will remember what address to use with any recipient and.

Unfortunately, some mail providers (like Migadu.com) block sending mails with "From" anything other than primary user address, even through they "support" catch-all. I was especially disappointed as that stopped me from using IDN mail address. I successfully created mail account using Punycode and I was able to receive mails with national characters, but their filter stopped me from sending.

I know IDN mail address is risky, but it's something I wanted to test. My surname contains non-ASCII character.

They indicated in January that they are working on allowing customization "From" filter customization, but it is still now available and contact with them is very difficult (they are not replying to mails unless you repeat question a couple of times). To be fair, I'm not paying yet (I wanted to test IDN works and it did not, so I'm not very interested in paying when they offer free account anyway).

[monkey34]

Thanks! I tried Thunderbird a couple of months ago and abandoned it because its UX seemed to not have really progressed in a number of years -- I hadn't used it since the Netscape Communicator days but it seemed... somewhat the same.

Although I realize these days a number of modern clients store copies of your email on their own servers for push notifications (or more nefarious) purposes, so maybe Thunderbird really still is the best option out there. Regardless, thanks for taking the time!