HA Mail Server

I'm researching setting up a 2 node cluster for providing SMTP/POP3/IMAP
services.  I'm currently running a HTTPD cluster so I understand all the
details of setting up the fail over etc.

The question I'm wondering about is what methods are the best for doing
this and the best way to manage the mail spool files. and whether I'd
want to use Fail Over or if I can use a Load Balanced configuration.

This shouldn't be too different than a HA file share, etc. but since
I've only dealt with rsyncing infrequently changing files to web
servers, this looks like it might be more complicated to maintain data
integrity. 

Any tips are appreciated, Thanks

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Jeff Bearer, RHCE
Webmaster, PittsburghLIVE.com
2002 EPpy Award Winner, Best Newspaper Website