NeoMutt is a command-line (CLI) email program that's flexible, powerful and efficient. It's a fork of Mutt and adds a lot of additional features to make working with contemporary configurations (e.g. IMAP/Gmail) more comfortable.
NeoMutt is a traditional MUA providing the ability to read, write and deal with mailboxes. Additional supporting utilities, such as Isync's mbsync, Goimapnotify and Msmtp, provide the features for a complete email system.
Plus there's the cute Mutt/NeoMutt logo! About the only thing I don't like is the ridiculous computer-language thing of putting a random capital in a WoRd.
I put this page and blog series together because like many CLI's the downside of the power is that it's complex to learn with a lot of possible configurations. My own learning experience was mostly cut-n-pasting other people's configs without really understand how it worked. In the blog post series I've tried to cover the foundations in an easy to understand way, and then progress to more complex configurations.
Sending email is covered in the series, with all the detail in the Msmtp tutorial page.
A few tutorial posts that I've found useful: