aerc-mail console
Other than it apparently doesn't have PGP support this terminal client is excellent, like mutt, and being made by SourceHut is a quality proof to be fair.

Alpine console
Turns out I've took some time to set it up and running with IMAP on this client.
It also supports NNTP which is a nifty feature so I can browse (and post to) newsgroups.

Claws Mail graphical
I used this one as my default email client, it perfectly fits my needs on a minimal graphical environment, it even has good OpenPGP support and I appreciate that. I recommend this client for day-to-day use.

Update #1: as of 4.x it now uses GTK+3 for the GUI and that made it look really weird. 
Update #2: Fortunately I can still use the 3.x version which uses GTK+2.

Evolution graphical
This is GNOME's view on an email client, which is more like Thunderbird, but looks apparently better than Mozilla's client. 
By far it's seconded by Claws on my rating. Good one I guess

mutt console
My default email client on a non-graphical environment, besides from aerc-mail, it also perfectly suits my needs, also, it has Vim-like keybindings so it's kind of a godsend to be fair. 
Excellent client, also has OpenPGP support.

(neo)mutt console
Couldn't ever get used to this client, despite it being backwards-compatible with mutt, never got it to load mutt's default .muttrc because of some syntax errors specific to neomutt, while in mutt it just worked as-is, weird.

Update #3: Actually, on second thoughts, configuring it isn't so difficult (both the .neomuttrc and the .muttrc are similar in syntax, but have their differences)

Sylpheed
I currently use this client on my host as a replacement to Claws, it's equallly as good though it seems unmaintained on upstream. It doesn't have as many features like Claws has, but it just works.

Update #4: I don't use this one anymore, returned to Claws. However, I may consider it again sometime
Update #5: I don't use graphical clients anymore, because I do practically everything inside a console

Thunderbird graphical
I once used this client, but as with anything, Mozilla ruins everything at its sight, and so it did with this client. 
How saddening. Never touched it again.