I can only send emails from my own domain

I recently added a new domain to my OS 10.5 Leopard Server machine and I can only send from my own domain, meaning I can only send emails if my users are the ones sending the emails, If I send an email from a hotmail account or Gmail or any other domain, they never arrive.

I can only send emails if the users are in the same domain for example:

My domain is www.mydomain.com, wich has users in the Open Directory as user1, user2.
When I create an email account for user1, user1 can send and receive emails as long as user1 is the sender. If user2 is the sender and sends to user1 user1 will receive it without problems.

If me@hotmail.com sends user1 or user2 an email they will not arrive at their destinations. If user1 or user2 send an email to me@hotmail.com, me@hotmail.com receives it.

Any ideas why this is happening? I already have under Server Admin, Mail service, Advanced, Hosting, the name of my domain.

Any ideas?

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nappy_dThere are a 1000 ways to skin the technology cat.Commented:
Do you have your server setup with an MX record in the public DNS domain?  Without this, your mail from external sources will never arrive because they do not know how to reach your server.
try dnsstuff.com (there are many such services, it just happens to be the one i use) and run a trace on the route of the mail and it will determine of you mx records need ammending or if your mail is being dumped due to broke rules
xcamaroxAuthor Commented:
This is more or less like my DNS looks online thru my Registrar... @ is the main Host... xxx.xxx.xxx.xxx is my static IP address.

 A (Host)  
 Host     Points To            TTL Actions
 @        xxx.xxx.xxx.xxx     1 Hour    
 mail      xxx.xxx.xxx.xxx     1 Hour    
   CNAMES (Aliases)  
 Host      Points To     TTL Actions
 www       @                 1 Hour    
 ftp             @                 1 Hour    
 MX (Mail Exchange)  
 Priority  Host    Goes To                    TTL Actions
 0             @      mail.mydomain.com       1 Hour  
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nappy_dThere are a 1000 ways to skin the technology cat.Commented:
is your firewall set to port forward to your mail sever?
you will neded to check your smtp with your isp for outgoing mail since it will be posting through your isp on the way out
xcamaroxAuthor Commented:
I am outside the firewall, so I dont think the firewall is the problem. Why would my ISP have nothing to do with this? Its my own domain and my ISP does not block anything because I already have another domain with the same ISP and different domain.
because your domain mail adress will forwarded through your isp and they will undoubtably have a sender policy framework in place as anything negotiating their outgoing server with a different domain will look like spam
xcamaroxAuthor Commented:
Domain registrar does not support outside hosting.

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