Hi,
This is totally empiric from my end-user point of view... to record the time it takes from start till ability to read first email message content (appearing in preview pane).
Small progresses observed but still much to do :-)
I thought it may be of interest to anyone curious or willing to dig into perf profiles to either help identify culprits in core, imap, caldav, or else... and raise separate related specific bug reports, and hopefully help reproduce them and sort them out...
Just a volonteer trying to help... in the hope it may somehow...as a small step forward... to improvie TB startup performance.
Cheers,
Richard