UVa was having significant problems with our big central SMTP
servers being used by various Internet bulk mailers to relay their
traffic and Spam the Internet. The problem was so bad that we
needed to implement an immediate solution. We checked with many
other sites and found that most were disabling relaying and teaching
their users to reconfigure their mail clients to use their ISP's
SMTP host. With our large population of mobile notebook users,
the
small size of our UVa modem pool, and large number of IMSP users,
this simply wasn't an option for us.
The solution we developed strikes a compromise between allowing
unrestricted relaying and turning off (3rd party) relaying
altogether. We allow each remote connecting SMTP host a fixed number
of messages per hour, after which, any additional relaying from
that host is blocked. The idea is to allow moderate relaying
that
satisfies our ISP-connected users, but enforce limits to discourage
spammers. We're finding 100 messages per host per hour works
well.
Note that the traffic limit is only on messages that originate off-
campus with recipient addresses that are also off campus.
We have not run into any user problems so far and the amount of spam
that our servers are relaying has diminished to almost nothing.
The
one potential problem would be with users who maintain a large
mailing list with many non-UVa recipients on a portable computer.
We haven't had this problem yet - if one occurs we'll get the user
set up with a real centrally managed email list.
