Personally, I use mu4e (part of the mu software) to read, organise, compose and send emails. It uses a text-based interface, and runs from within the GNU EMacs editor. Emails are stored locally in the Maildir format.

• It is actively maintained and open source, and not controlled by a company
• Apart from xapian and EMacs, chances are that you have the dependencies already installed
• Mails can be composed in HTML format, but this may take a few extra tweaks. (I do not do this myself.)
• Emails have to be stored in the Maildir format to be indexed using mu and viewed with mu4e
• Neither POP nor IMAP are directly supported. To fetch or sync emails from/with an external server, external applications can be called, like mbsync (for IMAP), offlineimap (same), or fetchmail in unison with a locally running postfix MTA (for POP)

I am not sure if I can recommend this solution, as it can be a bit technical compared with other email clients. For me, it is entirely worth it, though.

Why did Americans get these crazy ideas about monarchies? I am living in a monarchy that’s like ten times as democratic as the United States ever was.

Dillo and NetSurf