We have a server 2008 R2 with exchange 2010 sp1.
We have recently encountered a very wierd issue. When sending emails to a specific email userA@domain.com, the email is not received by the recepient, nor a error is returned. we received all emails sent by userA@domain.com, however we are not able to reply (emails simply do not reach)
On the other hand, sending emails to userB@domain.com, works fine
We have checked the issue with out ISP, which is the same ISP hosting the @domain, who claims to be a server problems.
After several checks on their side, they claim the mail request sent to userA@domain.com does not reach their MX server.
Any help is greatly apreciated