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Cannot relay SMTP from outside subnet

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3 replies

by jedavidow

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Our Exchange server is doing something weird:

The exchange server is behind a firewall, IP=192.168.1.1.

When a user ON the subnet sends an email thru smtp, there is no problem, the message is delivered no matter what the recipient.

When a user is external to the firewall, only messages to the Exchange server's domain get delivered. Any other emails (@yahoo.com, @whitehouse.gov, etc.) return errors that they cannot be relayed.

It is not a matter of Windows authenication, because there are subnet Macs with no authentication that have no problem sending mail.

This is not a firewall issue, because the messages get into the server, but it only won't pass on certain ones.

As far as I can tell, I have very low security on the smtp server.

Any ideas?

3 replies

by curlergirl

It sounds like your Exchange server has been set to prevent forwarding by external hosts. This is generally a good thing, and a common thing for Exchange admins to do, because it prevents your Exchange server from being spammed or used to spam someone else. However, it sounds like you've come across a situation where certain external hosts need to be allowed to relay. This can be controlled within Exchange - but not knowing which version you have I'm not sure I can give you exact instructions. In Exchange 5.5, I believe its on the Routing tab in the properties of the Server; I haven't worked as much with Exchange 2K, so I can't remember where it is. Hope this helps!

by jedavidow

I had a stupid setting in the access controls- I was only allowing mails sent from the subnets to be relayed. I forgot that I did this.

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