How do I configure MailEnable on Win 2k3 to allow Google to relay SMTP through it?

Question

We use "Google Apps for Your Domain" for email, but wish to use our old email server for sending mail. The reason being that Google Apps SMTP is blacklisted by several of our partners as being spam(!!).

Google has detailed instructions on configuring this option, but I'm not 100% familiar with SPF and certainly not experienced with MailEnable at all. MailEnable seems to force you to specify individual IP ranges to allow instead of ranges, even though I followed the instructions for configuring SPF, and browsed their knowledgebase.

I've tried setting this up, but MailEnable isn't allowing google to relay mail:

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. 
We recommend contacting the other email provider for further information about the 
cause of this error. The error that the other server returned was: 503 503 This mail
server requires authentication when attempting to send to a non-local e-mail address.
Please check your mail client settings or contact your administrator to verify that 
the domain or address is defined for this server. (state 14).

Any MailEnable advice on how to proceed?

Answer 1

This actually sounds more like the recipient domain's MX records are misconfigured. It's requiring authentication for sending to non-local e-mail addresses which they would normally require from their users who are trying to send a message outside the domain.

The MX records for the domain are pointing to particular servers to receive e-mail for the domain, but when you try to deliver to those servers, the servers are saying they are not responsible for receiving e-mail for that domain and thus require authentication in order to relay the message to the appropriate recipient.

Check to see which servers are responsible for the domain. If you are trying to send to alice@example.com, do the following at a Windows command prompt:

nslookup -type=mx example.com

You'll see a list of servers responsible for receiving mail for that domain. The list may contain the name of the provider that handles e-mail for that domain, say example.net. You may have luck messaging postmaster@example.net and tell them when you try to send to the domain you get the "requires authentication" response. Otherwise, you might need to lookup the whois records for example.net to determine the appropriate contact for the issue.

It might also help to contact the IT Managers for your partners to let them know about the problem and they may not be aware of the misconfiguration.