Some people are never happy

Part of my day job is to manage the central email systems for our site. We're a semi-large facility with about 4000 people here on a daily basis. We collaborate with other facilities around the world. A lot of this communication is by email so the system has to be reliable.
When it was first designed about 10 years ago we stated that internal mail would be delivered in under 15 minutes. In reality it took about 30 seconds but at that time we had some smtp to (name your low end mailer) gateways that usually accounted for most of the delay. Over the years the non-smtp based mail systems have disappeared and we're pretty much a IMAP based facility. There is a cluster of Notes users and some folks who like to read mail on one of the Unix systems but most have switched to IMAP.
We've also spent considerable effort rebuilding our core infrastructure. Multiple gateways, load balancing, redundant LDAP servers, etc. Throw in 2 levels of AV checks and spam tagging and the average mail message has several hops to make before it gets delivered. Still - the average mail message is delivered in under 5 seconds. If it's list mail it might take 30 to 45 seconds depending on how busy the list machine is.
Yesterday my officemate commented on how slow mail was. Thinking there might be a real problem I started looking. Then I asked exactly what the problem was. A message sent to the list took 72 seconds to be delivered.
Grrrrrrrrrr