We just finished successfully moving a 20K user sendmail setup to
What we did, in stages, is:
1) Create two external smtp in MTA's using qmail
2) Create a NSF mount located on a Netapps for /home/vpopmail/domains
3) Create all the 20K users on an SMTP OUT/POP host running
qmail/vpopmail using the mysql module.
4) Add chkuser on the external MTAs for user checking by having the
domains listed in rcpthosts and users/assign, but not in virtualdomains
5) Today we moved sendmail IP over to a qmail/vpopmail server and added
the domains to virtualdomains so the external MTAs do local delivery to
the NFS mount.
End result, we have the two external MTAs receiving, validating and
virus/spam scanning the incoming emails and doing local delivery for our
main domains (we're an ISP).
As well, we are now scanning user outbound mail for viri and spam which
we were not doing with sendmail.
Identical systems and the old sendmail server was running at 1.5 - 3.0
load. The new qmail server is running at 0.13.
Just thought you might be interested in the setup.