[unisog] Forwarding email and security.

Daniel Feenberg feenberg at nber.org
Tue Dec 6 14:44:37 GMT 2005

On Mon, 5 Dec 2005, Cary, Kim wrote:

> I've been asked to find out how other schools allow end-users to forward
> their email to external accounts (in our case, Exchange2k3 is the back end
> -- if anyone is doing this with Exchange2k3 I'd love a quick "how to"
> conversation).
> Given that task, I've also heard that autoforwarding email to external
> accounts is a security issue. Does anyone have any policy or technical
> safeguards to share related to that problem?

Some of the forwarded mail will be spam, and some of the final recipients
will complain to the destination MTA operator about that spam. The
operator of that MTA is likely to consider putting your MTA IP address on
his blacklist - it isn't really possible for him to tell that you are
victim rather than a perpetrator.

On newsgroups AOL is usually listed as the problem destination, perhaps
because they track user complaints rather than using spamtraps to learn
about bad mail sources.

Other than user education (and not continuing to forward to any user who
fails to learn) I don't know of any technical solution. AOL does have a
system for informing you of complaints, but they dropped me from the
system after one year with no complaints against our MTA.

That said, forwarding is usefull for many reasons. We have been forwarding
on request for years and have had no trouble from any destination MTA. We
no longer provide a webmail service - people wnat webmail we just forward
all their mail to gmail.com. Keep an eye on the blacklists, though. If you
start to show up on the aggressive one, take action, or you will start to
show up on the major lists soon thereafter.

Daniel Feenberg

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