Been working on folder index serialization for the past few days - this will let Iris display mail folder contents while offline or before the synchronization of messages from server is complete. So while a new connection to open an IMAP folder is established, Iris will load the headers from local storage in a separate thread.

For some speed benchmarks:

My INBOX folder with 3102 messages:
-[IrisFolderCache loadThread]: 459ms
-[IrisFolderCache saveThread:]: 260ms

MorphOS CVS mailouts folder with 12407 messages:
-[IrisFolderCache loadThread]: 2286ms
-[IrisFolderCache saveThread:]: 983ms

This is on my 1.67GHz PowerBook by the way.

Next step: incremental synchronization for IMAP, then sorting and filtering.