I've been using Thunderbird almost 20 years. It's about to start having a makeover, so that could be interesting.
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Thunderbird is and always has been the GOAT. The only real downside is the lack of a tray item, but this can be partially solved by installing Birdtray. I think Thunderbird 115 released with this feature, but it only works on Windows. Fingers crossed that it comes to Linux soon
Mutt. All mail clients suck, mutt doesn't.
Mutt + procmail = ❤️
Mutt is a console based client, so if you have to deal with a lot of html or image laden emails it can be a hassle. There's options for these things, mind you. You can call a text based browser to produce fairly readable text output within the client, or use an external application (browser, image viewer, etc.) to view it. Or anything in between. Mutt is extremely customizable. Just something to be mindful of.
That being said, I'm also quite happily a mutt user 😊.
Clarification:
I prefer neomutt with mbsync and notmuch. Mutt wizard can help you get setup. Pandoc is great for formatting, and any browser can be used to view html if lynx is not good enough.