Althea is an IMAP email client for X that uses the GTK widget set. It was built with the IMAP protocol in mind in order to avoid many of the pitfalls experienced by POP clients that added IMAP support. Althea allows easy access to a nearly unlimited number of servers, and has a very small memory footprint. As of version 0.5.0 Althea also supports IMAP over SSL.
The AMC Mail Client is a mail client striving to be a robust, fully gnome-compliant mail reader. However, the AMC Mail Client differs from other mail clients in that it attempts to utilize existing tools for mail retrieval, sending, and filtering, (fetchmail, sendmail/smtp, procmail). By not going through the process of reinventing the wheel, the AMC Mail Client starts out as a fully equipped client that inherits all of the features of these existing tools.
Arrow is an elegant, powerful, graphical interface to electronic mail. This is not just another single window mail reader. Instead, it displays each mailbox and message in a separate window, thereby allowing one to simultaneously open as many mailboxes and view and compose as many messages as one wishes. This paradigm also allows one to drag-and-drop text between messages and organize ones mail by dragging messages between mailboxes.
Evolution is the GNOME mailer, calendar, contact manager, and communications tool. Evolution represents the next step forward in GNOME applications. The tools which make up Evolution will be tightly integrated with one another and act as a seamless personal information-management tool.
getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
GMailWatch is a GNOME Panel Applet that displays a summary of incoming mail (sender/subject) rather than just an icon. It's similar to the old xmailwatcher utility (and uses some of the same code), and is also based upon mailcheck (of gnome-core). The user can change the size of the panel applet.