E-Mail scaling question

[Mark Moellering]

Hello All,
My company needs a [new] e-mail solution for a product rollout.  Rather than 
have a few e-mail domains with lots of addresses, the solution we need is for 
a very few (mostly one, very rarely more than 3) accounts on upwards of tens 
of thousands of domains.  

I can't find any info on scaling sendmail or postfix to this many domains.  If 
anyone has any info, knowledge, horror stories, etc. It would be greatly 
appreciated

Also, I am assuming that to play nice, we need a dedicated IP per domain, so I 
may have to survive setting that up before I even get to the e-mail.  If 
anyone knows of a legitimate way to set up an e-mail domain on a shared IP and 
not have half of the e-mail servers assume we are spammers, let me know.

Thanks in advance

Mark Moellering
classcreator.com