resolving to a nonexistent mx record

Sorry if this ends up being the wrong list, but it seems like it's a DNS
issue somewhere.

The DNS servers in question are latest 8.x. When my users send email to
@twcny.rr.com 2/3 of the time they receive NDR's back saying: Connected to
24.92.226.159 but connection died. That IP resolves to nymx02.mgw.rr.com. I
dig twcny.rr.com for mx records and that doesn't exist. RR tells me that
used to be one of their MX's but no longer. They didn't know how long ago
it changed. I've dug on their name servers, all my name servers, and others
and none give that as an answer. I thought it might be cache, but I've
restarted my named processes and still this happens. I know I'm missing
something here, but I cant figure out what the hell it is!

Any direction on this matter would be great! Thanks!

mike