myhostname = RPCSERV1
this IS the real hostname?? isnt that ok?
Thats not ok. For email, you have to use a real existing hostname and it may not be identical with a hosted email domain. Use something like:
where you replace yourdomain.com with a domain name that you own. Then make sure that the subdomain mail.yourdomain.com exists in dns and that it points with a DNS A-Record to the IP address of your server.