Are you having a problem configuring Microsoft SMTP Server built in to Windows Server 2003 and Windows Server 2008? Are your emails being sent out successfully to all domains other than your own?
This is a common issue that is caused by a misconfiguration of the Microsoft SMTP Server. This issue normally occurs when you configure the web server SMTP Server domain to be the same as your own email domain (which it should be) and your mail is hosted somewhere other than on the web server.
The cause of the mail not arriving at your domain is due to the SMTP server domain being configured as a ‘Local Domain’ which causes the web servers SMTP server to think it is the actual mail server your domain and does not send the email out over the internet, it ends up in the drop folder which is normally located at c:\inetpub\mailroot\drop\.
When your mail server is hosted somewhere other than on your web server, you should configure the web server SMTP server domain as a ‘Remote Domain’ which will cause the mail to be sent out over the internet and your problem should be solved. See Microsoft’s explanation below.
A local domain is a DNS domain that is serviced by the local SMTP server. Any message with a local domain name that arrives at an SMTP server must be delivered locally to a Drop directory or returned to the sender with a non-delivery report (NDR). Local domains are sometimes referred to as service domains or supported domains. E-mail addresses with local domain names are often referred to as local addresses.
If the domain is local, you can designate it as default or alias. There is one default domain. It is used to stamp message headers that lack a domain specification. An alias domain is an alias of the default domain. If you add a domain and assign it as the new default, the previous default changes to an alias domain.
Domains that are not local are known as remote or nonlocal domains, and e-mail addresses with remote domain names are referred to as nonlocal addresses. The SMTP service looks up remote domains in DNS.
If you want to set unique delivery requirements for a specific remote domain, you can add a remote domain and configure it accordingly. For example, you can add a remote domain and require that the SMTP service always use Transport Layer Security (TLS) encryption in sessions with that domain. Or, you can change the routing so that messages sent to one remote domain are routed to another remote domain. Use the Domain Properties dialog box to configure domains.
For more information, please refer to: http://technet.microsoft.com/en-us/library/cc738146(WS.10).aspx