This morning we are seeing delays with email of several hours. The DNS server stopped responding which caused the mail server to not know where to deliver its mail, resulting in the mail being spooled. We have restarted the DNS server and mail is flowing through but there is a fair sized backup of mail in the spool which will take a few hours to catch up. We saw this same behavior last Friday evening as well. To prevent this type of failure in the future we have put a process in place to verify that the DNS server is responding properly and if not, it will automatically be restarted.

My apologies for the mail delay again.
-tom