I reject your e-mail

I've always heard that the correct behavior of a mail server is to reject e-mail for local undeliverable addresses rather than accepting them and then bouncing. I never put too much thought into it though until recently when I took over management of our e-mail infrastructure.

When the systems were handed to me, their queues generally had about 800-1000 e-mails
to be delivered at any given point. As I dug into why, I found that the majority of those e-mails were outgoing bounce messages which were undeliverable for one reason or another.

After a few changes, those systems are now rejecting around 1,000,000 spam messages a day. These are messages that would previously have been accepted and sent back out on the internet as backscatter.

Rejecting instead of bouncing allowed me to significantly cut down on the amount of processing power, bandwith and disk space used on these systems. Not to mention cutting down on the amount of e-mail that the backscatter victims were receiving.

Now if only everyone else who runs mail servers would figure this out.