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Cannot relay SMTP from outside subnet

By jedavidow ·
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?

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Cannot relay SMTP from outside subnet

by curlergirl In reply to Cannot relay SMTP from ou ...

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!

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Cannot relay SMTP from outside subnet

by jedavidow In reply to Cannot relay SMTP from ou ...

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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Cannot relay SMTP from outside subnet

by jedavidow In reply to Cannot relay SMTP from ou ...

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