Multi Domain Email Server Configuration

My question is general, more for best practices.

I have an Exchange 2003 server configured to receive email for 2 email domains.
Half of my users send out as the other half as, meaning this is their primary email address and the reply to address.
The server has a single Virtual SMTP Server and sends outbound email via Postini Smart Host. Postini knows about both domains as well.
I have a PTR created with the ISP for the serves external IP = also has an SPF record created. has no SPF record (yet, I'll create one soon)

The users seem to have trouble sending email from time to time. I'm wondering if I should change the way this is configured. Maybe make a Virtual SMTP Server for each of the email domains?

Thanks for your thoughts!
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What kind of problems do they have. I have a similar setup where we have 8 different domains that my users send from and we don't have any issues.

All of our mail is sent through a security service for spam and virus scanning, so that may make a difference.

You don't need to create an additional Virtual SMTP Server, this will add to your complexity. I would create an SPF record with the scope of mail servers that Postini use and don't forget the line "".

Postini are delivering messages perfectly well, your issue is with the origins of the message which is probably failing on the SPF check. Positini will tell you the same too. If you create a valid SPF record this will resolve and authenticate any issues of delivery or possible delays.

Best of luck!

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