Barracuda Networks Spam Firewall

Per Gregers Bilse bilse at
Tue May 18 23:44:57 UTC 2004

On May 18,  5:22pm, Valdis.Kletnieks at <Valdis.Kletnieks at> wrote:
> > Once AOL starts doing it -- you can bet they will be one of the ones 
> > blocking on it.
> That's going to pretty much torpedo the concept of secondary MX's.

Not to suddenly burst back, but ...

Second/terti/etc-ary MXers really belong in a bygone age anyway.

There was a time when IP was a novelty, and UUCP was king.  Then there
was a time when UUCP was getting long in the tooth, but politics
dictated an IP Internet that was not universally connected.  Somewhere
in the meantime, leading a life of its own, was something called
FidoNet ( and something else called BITNET
(, but as of today both are for pub brawls only.

This is of course an opportune moment to recall that the 10th anniversary
of the shutdown of the successor of mcvax.bitnet, namely mcsun.bitnet,
was in January of this year.

The fundamental idea of less preferred MXs was to get the mail delivered
through a backdoor, not reachable via IP routing from the originator.
Think multihoming for email, keeping in mind that email routing is
disjoint from IP routing: a genuine secondary MX would be able to,
one way or another, deliver the mail, by means not accessible to the
originator.  This inaccessibility would be because the more preferred
MX was unreachable for one of several reasons (host down, network down,
or politics enabled), but, whatever the reason, one wanted to find a
way of routing around the problem.

For a long time since then, backup MXs have been seen as a kind of
value-added courtesy service; they serve no really useful purpose,
but look good on a checklist.  In practice, of course, in the current
Internet it rarely matters on which host an undelivered email is spinning
in the spool area.


  -- Per

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