Securing SMTP on Exchange 2007

CaringIT used Ask the Experts™
Our Exchange server is sitting on our network and has SMTP open on the firewall - but it is allowing anonymous sending of emails.  We have stopped relaying via SMTP, but need to know how to stop this issue.

Can anyone help?
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If we remove the Anonymous option from the list of permissions to send, what impact would this have?

We have one connector for general use which has it on and one for a system internally specifying internal addresses that has it on.
It means any applications which do not authenticate to the domain first can not relay i.e. you can not relay without authenticating first to the exchange server which means specifying domain/username and password
Ahmed AbdelbasetInfrastructure Architect

leave default one without anonymous and create one more for appliction with anonymous permission for only remote Ip address of applictation server in network tap on new receive connector for application.
By default, the Receive connector that ships with Exchange 2007 does now allow 'Anonymous submission' connections and it certainly will not allow 'anonymous relaying' unless you have changed the authentication type to 'Externally secured', which you wouldn't do on a receive connector that is available from the outside world.

Anonymous permission needs to be selected if you want to allow external users to send mail to the receiver connector, and unless you have selected 'Externally secured', they will only be able to send mail to domains on your Accepted Domains list.


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