Following the example of GKH and others, I’ve added one more piece of software on my email setup and workflow. That piece is msmtp, a very simple and lightweight SMTP client, that integrates really well with the rest of my setup.
At its core, msmtp does one thing. It gets mail from a MUA -in my case mutt- and relays it to a remote SMTP server. Its strength lies in its configuration file. All of its options can be set per account, which means, that it’s easy to achieve complex tasks. E.g., you can have two accounts use no proxy, a couple more use a remote machine through a SOCKS proxy and a super private one use TOR.
Another thing I really like about it, is the “fine tuning” it allows you to do in regards with TLS. It gives you the ability to pin TLS certificates to each account or even set the minimum number of Diffie-Hellman prime bits for TLS sessions.
There are also some scripts based on msmtp that allow you to queue emails if you don’t have internet access, e.g. when on a plane, review them later on and send them once you’re connected again.
All in all, if any of the above sound useful to you, give msmtp a try. I promise you won’t regret it.