In fact, we've currently got the MTA (it's called simta) set to limit itself to 250 inbound SMTP connections. We monitor the SMTP interface (and the LDAP interface) to ensure that it remains responsive. Our customer expectation is that when email is sent, it will arrive at the UMich recipients mailbox within seconds. In short, the concurrency reflects how our users send & receive email.
<http://tools.stanford.edu/cricket?target=%2Fldap%2Fbinds-mail>
So I'd say that keeping 250 connections open per server is extreme overkill.
--Quanah
-- Quanah Gibson-Mount Principal Software Developer ITSS/Shared Services Stanford University GnuPG Public Key: http://www.stanford.edu/~quanah/pgp.html