Re: smtp redirection

[Bruce Hudson <Bruce.Hudson () DAL CA>]

> We are redirecting smtp traffic inbound to some campus mail servers via MX
> records in our DNS to an anti-spam appliance (Bluecat Meridius) and find
> some email circumvents the appliance apparently by using DNS IP lookup for
> host resolution and not using MX records to send mail to mail servers on our
> campus. The vendor recommends blocking inbound port 25 to the campus mail
> servers from the internet. I favor this approach. However the mail folks are
> concerned that some legitimate email may be dropped this way.
>
> For those of you who redirect email to an anti-spam device; how are you
> doing this redirection and how are you dealing with the spammers who
> circumvent the MX record approach?

    I would say that for a central anti-spam system to work, an access list
that forces mail through it is absolutely required. Voluntary MX records
will fail because spammers just do not play by the rules.

    We used to add A records for our mail domains for years to take care of
the odd broken mailer that did not understand MX records. We stopped 6-7
years ago and I have not heard of any major problems. By definition, any
mail that ignores an MX for delivery is not legitimate. You can only support
broken software so far.

    For client mail that needs access to the internal servers we offer a
submission service that requires authentication on port 587 and a VPN that
will bring the client systems into the internal network.
--
Bruce A. Hudson                         | Bruce.Hudson () Dal CA
UCIS, Networks and Systems              |
Dalhousie University                    |
Halifax, Nova Scotia, Canada            | (902) 494-3405

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