On Tue, 05 Jul 2005 21:27:23 PDT, Justin Mason said:

BTW, someone (possibly Randal L. Schwartz) came up with a neat related trick to the above -- set up an interface alias on *the same machine* as the primary MX, list that as the last MX in the list, and (assuming that the software side of the primary MX is reliable) you're then assured that any SMTP traffic that arrives on that IP's port 25 is spam, since when the primary MX's hardware goes down, this MX will, too.

That's got the same failure mode - if I take a 30-second hit and can't reach the first MX, then the link comes up before I try the last MX, I hit the "bad" one. And since the link burp is at *my* end, you don't even know about it, unless you hook it into a full BGP feed with Zebra or something and see AS1312's routes flap (and even then, it's dicy - a very short burp may not cause the routes to be withdrawn)....