I've written about this before, but I used to run my own mail server and it's no cake walk.
I used to do greylisting with spamd and ended up silently losing quite a lot of email. (Many mail hosts do not re-send from the same IP, meaning messages essentially get stuck forever.) Doing spam checks at DATA time and rejecting obviously bad emails outright seemed much more effective and less dangerous. I never managed to get Spamassassin to do this, but auto-rejecting languages you don't read also cuts down on spam a lot.
(I missed out on a consulting opportunity because the client's host of choice seemed to be a known spammer and my mail server's filtering was too aggressive about trusting blacklists. I chose to silently-reject those types of messages, so nobody got a bounce. Fortunately, someone was nice enough to ask me about it out-of-band so at least I was able to turn off greylisting and blacklisting before losing much more mail.)
I never found an imapd that scaled to having a lot of messages in a folder, so I ran a cron-job to move mail offline after 2 weeks (for mailing lists) and 1 year (for INBOX). Similarly, I never found a good client to use; Gnus had a very cryptic configuration that I could never believe worked, and mutt was not Emacs-y enough. Reading my email mostly consisted of waiting for Gnus and deleting spam. (I never figured out a good way to get Gnus to move messages marked as spam somewhere so that I could run a cron job to automatically train Spamassassin on the known-bad emails.
For search, I used HyperEstraier: http://sourceforge.net/projects/hyperestraier/
You set it up to run the ingestion program as a cron job every 10 minutes, and then you get a CGI that will show you matching emails for your query. Of course, you can't actually click the links and go anywhere unless you set up some sort of web-based email viewer. I never found anything I liked so I lived without webmail. (There are lots of options. All difficult to configure and probably riddled with security holes.)
Once your server is up and running, you need a secondary MX and a backup plan for your email. (I used Dyn.com's secondary MX hosting service. A lot of spam comes in through the secondary MX, so you can't just implicitly trust it. This involves more configuration.)
Finally, spam filtering uses a lot of CPU and RAM, so you have to pay for a rather expensive virtual machine. Linode's $40/month plan seemed mostly adequate.
I don't really like composing email in the web browser, but I've gotten used to it and $5/month for Gmail and $0/month of my time screwing around with spam filters seemed like a good tradeoff.