What Trojitá is not:
A full PIM suite. That's something which we leave to other applications, so you won't find a fully fledged calendar in Trojitá. But you might help us make Trojitá a part of a fully-fledged PIM if you're interested.
A POP3 client. Trojitá works by accessing a remote mail store over the IMAP protocol. POP3 cannot work this way for technical reasons.
Finished yet. If you try Trojitá yourself, you will notice that some "obvious" features are missing. We are working on getting them fixed, but we could definitely use a help.
Some highlights of Trojitá are:
A pure Qt4 (and Qt5!) application with no additional dependencies
Robust IMAP core implemented using Qt's Model-View framework
Standards compliance is a design goal
On-demand message list and body part loading
Offline IMAP support
Support for bandwidth-saving mode aimed at mobile users with expensive connection
IMAP over SSH -- in addition to usual SSL/TLS connections, the server could be accessed via SSH
Safe and robust dealing with HTML mail