Damn email issues again!

Okay so this tie I send out to a long list, all broken into small groups in separate emails, I got over 110 retunred emails saying : Error 5.1.2 Bad Destination Host: “DNS hard error looking up [domain](MX)NXDomain)

From what I can see it is from a host that cannot be found (duh) but teh addresses are ALL domains that I have sucessfully sent to before (even the same small groups of names C&P’d from past sent emails into a BCC field).

Most are Shaw or telus but private domains are there too, NOTHING went through it seems.

any ideas?

ISP and HOST is Shaw cable, not a local mail server.