[CentOS] Dovecot Sending Slow down

I moved a hundred or so additional hosting accounts to one of my centos 4 servers. It was doing great before with like 50 accounts.

Anyway, since doing this sending email has slowed a lot. I have not done anything with the default settings in dovecot beyond the basics of what services and such at the top.. Server loads are running under 1. Disk IO is generally under 10%, ram no problem with no real swap used. I'm running dovecot in conjunction with sendmail.

Anybody have any ideas about what appears to be slow authentication... basically the mail client takes 5 to 15 seconds to connect and send. And this is from within the network. I suspect it is about the same from the outside.

Thanks, John Hinton