The common reference for a MUA, this is the program you run on your computer to talk e-mail.
Evolution, MozillaMail, KMail, Sylpheed
Outlook, OutlookExpress, Eudora
SquirrelMail, IMP, Outlook Web Access
Relevant standards include RFC:822 (or the updated RFC:2822), and MIME
31 pages link to MailClient: