So one of the things I've noticed, using KDE for quite a while, is that, while Konqueror, Kopete, Dragon, Dolphin, System Settings and several other applications open *when I click on them*, Kontact seems to start only after a very, VERY long time after clicking to start it. KAddressBook and KOrganizer don't take nearly as long when launched separately, but KMail seems to be the main culprit when it comes to very slow start-ups, and I feel it's about time I asked why. Additionally, is the new (rewritten?) KMail going to be faster at starting up, and by extension Kontact with the new KMail embedded?

My observation is that it has only been so for the last few weeks. Something has changed things, for the worse on my system at least, in recent weeks. It was said somewhere else that stopping the Akonadi despatcher-agent helped this, but it doesn't seem to make any difference here - unless, of course, it requires a reboot to enable reading some configuration. Certainly logging out didn't do it.

KMail is even under best circumstances a bit slower on startup due to having to deal with a lot more data, split over a lot more files (thus getting hit by harddisk delays a lot more than other programs).

A huge difference usually means that it thinks it can't rely on its index files (cached information, etc) but has to rebuild them from scratch, i.e. by reading all emails again, at least partially.

The reason for this to happen on every startup is not known yet. It seems to depend on a combination of factors because it does not happen for a lot of people but always happens for those who experience it.

In case you normally let the session logout quit KMail, try quitting it explicitly before logging out and see if this makes any difference.
You can even try to quit (once it has finished reindexing) and the restart within one session.

Since the question was brought up whether this would improve in th future: I am certain it will. Reason is that next version of KMail (hopefully finished in time for KDE SC 4.5) will be based on Akonadi, which does not use this kind of index files, thus will neither have to rebuild them nor read them on startup.

Cheers.
_

Thanks for the rather informative answer - it's something I've always been curious about, but I've put up with it anyway: thunderbird isn't much better, nor is it as comprehensive as Kontact...

Since I have this problem combined with long freezes when sending messages, I've been doing a lot of monitoring, to try to find the cause(s). In fact I think the same thing causes both situations. Nepomuk takes more than half of my CPU capacity for a minute or more when starting up kde-pim, and almost as long when sending a message through kontact. Using KMail stand-alone seems to cut the time of the freeze to around half a minute. You might like to try having ksysguard open and watching nepomuk activity yourself.

I've discussed all this with the developers, and they plan to talk about the issues at this weekend's sprint.