I've been in the process for the past week or so rearchitecting and installing a comletely new mail delivery, relay, and filtering system here at UMBC. The existing system, while flexible, had a lot of unnecessary overhead, had become hard to maintain, and wasn't up to the task of handling our current email load in a timely manner.
The new system was put into service during Thursday and Friday of last week, and with the exception of some very minor configuration problems, has been working flawlessly.
The new system consists, on the hardware side, of 5 sun v20z servers running Solaris 10. These servers comprise our email filtering (milters), mail delivery, and outgoing mail relays all in one system. Previously, they had been split up in different clusters, each communicating with each other over the network. The new configuration will allow for less servers to manage, less overhead in network communication, and therefore faster delivery.
Some design changes made to the queueing configurations should lead to a more predicatable and more repsponsive email delivery system, for both on-campus and off campus email usage.
As part of this upgrade, changes were made to other OIT systems which relied on the mail filters -- remedy.umbc.edu, listproc.umbc.edu and alumni.umbc.edu -- which accept mail via SMTP. Their DNS and local configurations have been changed so that all incoming mail must come through the 'mxin.umbc.edu' mail exchangers first, and then get forwarded on to the appropriate system listed above. These servers will only accept SMTP connections, in turn, from the mxin cluster itself -- any attempts to connect directly to them from other IPs will result in a "452 4.3.2 Too many open connections." error. If you're receiving this error, the system sending the mail obviously doesn't understand the concept of MX records.
This change can also allow us ot "filter" other campus systems' email through our virus filters with a pretty simple configuration change. (this is not a commitment to do this, just sayin....)
I'm frantically working to document all of the changes in the Mail Delivery section of the wiki.