M+ 1m - Download and install the M+ 1m free font family by M+ Fonts as well as test-drive and see a complete character set.
Roundcube - Web-based IMAP email client
Inconsolata - OSX, Productivity, Design, Typography, powerline, and Fonts
HEY - Email at its best, new from Basecamp.
Bitstream Vera Sans Mono - Bitstream Vera Sans Mono Font | dafont.com
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.