I'm unaware of any big-time ISPs that don't have email problems from time-to-time. I include my institutional mail system in that statement. Hackers, spamers, spoofers don't help. These mail and embedded systems do not run themselves and take constant attention. routers domain name system circuits mailing list manager mailers smtp client smtp servers authentication systems anti-spam filters upgraded software all get in the way of reliable delivery from time-to-time. /Pete