Spam and extra MX records

[Neil Joseph Schelly]

Not linux-specific persay, but mail and DNS servers can and do run in Linux, 
so I figure I'm more on-topic than usual.  I'm curious what opinions others 
have, especially negative about a strategy to prevent spam from coming into 
your mail server.  I've read a couple suggestions which make a good deal of 
sense to me, but just feel wrong.

1 - Set a fake MX record for a nonexistent server, or for a server that won't 
listen on port 25 for your _highest_ MX value.  Since a lot of spam will skip 
your lowest MX (primary) right away for a less-loaded backup MX with 
potentially less reliable spam filtering in place, the assumption is that a 
lot more spam will make it through a backup MX.  I've already confirmed that 
that does happen a lot.  The theory here is that by setting a non-operational 
backup MX record, spam bots will try and then give up on sending spam your 
way.  Real mail should never try the fake MX record unless all your real mail 
servers are down, in which case, you've got other issues to worry about.

2 - Set a fake MX record for a nonexistent server, or for a server that won't 
listen on port 25 for your _lowest_ MX value.  Essentially, this would make 
it look like your primary mail server is always down and every incoming 
message would have to get retried to your first "backup" MX. Again, the 
assumption is that spam bots will give up after failing to send to the first 
MX they try, whereas real email will try your next higher MX record in 
priority until it completes a delivery.

I'm curious if others have implemented these strategies and if they've ever 
gotten complaints from other mail administrators for any increased load.  I 
can't imagine it would be noticed honestly and the logic of making it work 
sounds promising, even if it is just a pretty bad hack to fool spam bots.  
Has anyone ever run into problems with this sort of arrangement?
-N