Gaze is a lightweight Gmail checker that sits in the system tray and notifies you of new messages in your inbox. You can configure how often the program will use the ROME API to check the Atom RSS feed for your inbox, as well as optional combined notifications, custom browser actions, theming, and more.
Mailpictures is a Nautilus extension in GTK/Perl, designed to be a more featured nautilus-sendto replacement. It allows direct access via Nautilus context menus, automatic resizing of pictures, setting for JPEG compression, ZIP archiving of the selection, support for Evolution, Thunderbird, Icedove, and Kmail, and the ability to save results in a folder.
DKIM-Verify is a software application that can provide DKIM verification for non-DKIM-aware MDAs. Using DKIM-Verify, which functions as a "wrapper" for the MDA, mail originating from and destined for the local domain can be verified. In addition, DKIM-Verify can integrate with mailing list software to provide verification of messages received for later distribution.
Yasma (Yet Another Sendmail Logfile Analyzer) is a reporting tool for sendmail log files. It provides a nice overview of your mail traffic like: messages transferred, some average values, top lists of messages sent, received, rejected, etc., and top lists of supposed spammers, status messages, relay hosts, and mailers. It analyzes one or more log files from the command line and writes an HTML report. For security, it can hide the user part of mail addresses listed in the report. A GeoIP database can be used to show country information.
Trojita is a Qt IMAP email client. It is a pure Qt4 application with no additional dependencies. It has a robust IMAP core implemented using Qt's Model-View framework. Standards compliance is a design goal. It has support for bandwidth-saving mode aimed at mobile users with expensive connections. In addition to the usual SSL/TLS connections, the server can be accessed via SSH. It has on-demand body part loading, offline IMAP support, and safe dealing with HTML mail (actually more robust than Thunderbird's).