Email Domain Blocked??

A family member in Austria is having her emails to me rejected by Comcast.  This happened a few years ago and I was told by a Comcast rep that her entire email domain, AON.at, was being blocked by Comcast due to spam.  He unblocked the blocked IP addresses for me but said they could get put back on in the future.   Is that what has happened?  If so, it seems a rather "blunt instrument" way to deal with spam.   AON.at  is A1 Telekom, the largest provider in Austria - hard to believe that I can't get email from their customers.

Thanks,

George