Yes, it was a fairly weak hypothesis. OTOH we got on several RBLs a number of times and managed to get taken off them. Once I added an SPF record it hasn't bee

Yes, it was a fairly weak hypothesis. OTOH we got on several RBLs a number of times and managed to get taken off them. Once I added an SPF record it hasn't been a problem since. Didn't use SPF to begin with because there was a large number of hosts legitimately sending mail for the domain and it was a pain to get all of the IP numbers for various crazy reasons.