SMTP Problem

Hello All, I've been stuck on this problem for the past three days. I recently configured SMTP on IIS. Everything seems to work fine when sending email to outside accounts (yahoo, hotmail, and etc.) The probelm is when I can not send email to my organization (Local). My company is using Mercury as an SMTP Client. I believe that Rely in enabled. Also, in IIS I believe that the DNS is also correct. HUH?????

Any help wou8ld be greatly appreciated.

Thanks in advance........