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Our corporate email is hosted on Google Apps, along with 5 domains for various products. Internally (Behind our firewall, not exposed to the internet) we have an IIS server running Microsoft ESMTP MAIL Service, Version: 7.0.6002.18264

This SMTP server is only used for internal applications to message users in the organisation, backup alerts, scheduled scripts notifying admin accounts, etc...

It has worked for many years, but as of last week, stopped working, the message I am getting is FROM google, when my SMTP server attempts to deliver to the end user, I am getting

Final-Recipient: rfc822;username@legitimatedomain.com Action: failed Status: 5.5.0 Diagnostic-Code: smtp;554 Relay Access Denied - psmtp

Wireshark

So my SMTP server is accepting it, trying to send it to google who hosts the mail account, and it stops there, with google's mail server saying the relay is denied.

This makes my SMTP server send ALL mail to the badmail folder.

The messages contain no spam content, and in fact one of the processes is the Google Apps Sync for Active Directory integration reports, so a google product configured like their integrator left it.

So I can only assume google implemented some new criteria on what is and is not acceptable for other SMTP servers to be allowed to send mail to them, but I cannot put my finger on what.

Nothing in our configuration on most of this has changed in years, and it has sent hundreds of messages daily during that time.

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The issue ended up being that a DNS server in the network actually had entries for when it was originally installed that were directing MX look ups to the old postini addresses. We never noticed because mail from that server was making it through. I was looking right past that at the error and ignoring WHO was responding. Deleting those MX records and allowing the SMTP server to query the public MX records routed to the correct ASPMX.L.GOOGLE.COM, ALT1.ASPMX.L.GOOGLE.COM, etc.

Funny, the answer was staring me in the face the whole time in the packet capture, it was just not what I was actively looking for :-D

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I assume the domain name in the MAIL FROMand RCPT TO commands is the same and registered in Google Mail. The problem might be that Google Mail doesn't accept mail that comes from outside and has a known domain as a sender. "Hey! You are not me! I"

Things to check out:

  1. Is your internal mail server permitted in your SPF record. Validate your SPF.
  2. Is your internal mail server configured as Inbound mail gateway in Google Apps.

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