Whether your server is in a Microsoft workgroup or Microsoft domain makes no difference in the world on whether it can send email.
Whether an MX record exists for a domain makes no difference in the world whethere a machine can send email -- an MX record specifies only where an internet domain receives email.
Before you distract yourself with testing all the wrong things, create yourself an account at some free internet email hosting company. Reconfigure your app so that it sends email to that account. Run your app.
If the email arrives, then your app works correctly. If it does not, I recommend you first test the correct functioning of your DNS settings on your web server. Here's the questions you should be able to answer, in order:
[ol][li]Get the IP address of the DNS server your web server asks for domain resulution.[/li][li]Using nslookup from your web server to the IP address of the DNS server you got in the previous step, can you retrieve the MX record of the mail server at the free hosting company?[/li][li]Using nslookup or ping from your web server, can your web server get the IP address of the server reported as the MX record of the domain of the free hosting company?[/li][li]Using telnet from the web server, can you make a connection to the IP address of the hosting company's mail server's IP address on port 25?[/li][/ol]
If you can do all of these things, and you app still isn't sending email, it's not a DNS issue, but rather a problem with your mail server or a programming problem in your app.
If and only if all of the above gets worked out and you want to send email from your app to an address in your own domain, there are three steps to get working email receiving at your domain:
[ol][li]Figure out what the servers of authority for your domain is/are. Whois is good for this. If whois is not working, perform a NS-type query in nslookup to "a.root-servers.net" or "a.gtld-servers.net".[/li][li]On the server(s) what was/were the answer to the previous question, creatre an MX record for [any arbitrary server name].yourdomain.com with an arbitrary priority. This can be mail.yourdomain.com, smtp.yourdomain.com, foo.yourdomain.com, bar.yourdomain.com, or sdfasdlkfjasdlkfjasd.yourdomain.com. It doesn't matter what you pick -- the fact that the MX record exists and points to that server makes email receiving work.[/li][li]On the server(s) that was/were the answer to question 1, set up an A record to resolved the address of your MX server. If in set2 you set up "sdfasdlkfjasdlkfjasd.yourdomain.com" as the MX record for your domain, then you must have an A record and an IP address for "sdfasdlkfjasdlkfjasd.yourdomain.com".[/li][/ol] ______________________________________________________________________
TANSTAAFL!