Hi all,
My client has an issue where random senders within, and outside of the organization will receive a "Remote Server returned '500 5.3.3 Unrecognized command' error when sending mail to a certain address. This only happens with one particular user. We checked the firewall and made sure smtp filtering wasnt enabled, made sure AV wasnt filtering as well. Sent test emails from external email and internal, can't replicate this issue. It happens randomly.
I am running Exchange Server 2010 Standard service pack 1. Does anyone have any suggestions or input on what may be going on?