I am stuck with this issue for long and trying to find a solution
many spam emails get through to existing mail boxes in exchange but some genuine work related emails senders complain about below mentioned error
"550 5.7.1 recipient not authorized, your IP has been found block listed"
when I check the SMTP receive log i see that recipient email address is known he/she is a existing user in the organization.
I am wonder the reason why exchange is throwing such error when its recipient and sender both are genuine and do not contain spam or meet the SPAM criteria.
awaiting prompt response on my query.