A MailClient for Windows and MacOS. (MailClients for these systems tend to be a cross between MUA and MTA.)
Made by 
Qualcomm, who seem to be concentrating more on mobile applicances (cellphones etc) these days.
Three modes of operation; light (free and less features), full with ads, or full for $40US.
One page links to Eudora:
lib/main.php:944: Notice: PageInfo: Cannot find action page