I've had a few oddities too , recently , using my NTL Address.
to Plusnet - finally delivered after 11 hours
YET sent within a few seconds of the above - to New York address with no delay , and delayed going to another UK address.
Then shortly after the Plusnet one was delayed , another to the New York address was delayed - don't know if it has got there yet .
Have ended up if I suspect a delay sending a copy by Mobile.me - no delay with it
No problems with incoming NTL addresses e-mails
If a thing ain't broke --- DON'T FIX IT
Experienced in making a mess of things
2 x MacBook Pro on OSX 10.6.4 ,Belkin N Wireless Router , [ sssh - and a PC wired lappy using XP Pro ] all on Virginmedia