NAT port 25 to 587 for an SMTP application

[de fl]

We have 2 network devices that use open relay (port 25, no authentication) to send status emails.  Our internal mail server requires authentication to send email over port 25.  How can we get these 2 devices to send email.  Can I forward the port 25 requests from the devices to port 587 on the mail server?  

[Jon Marshall]

If you are asking can you translate the port then if you have the right equipment then yes.

If you are asking whether sending it to port 587 will mean the e-mail is accepted then no idea :-)

Assuming the first is there a router between the mail server you want to send the e-mails to and those sending the e-mails.

Need to understand the network layout.

Jon

[de fl]

Thanks Jon!  We are trying to translate the port.  Both devices are internal.  The devices are on separate subnets with a Layer 3 switch in between, which is doing the routing.  

[Jon Marshall]

What is the L3 switch ie. what model.

The majority of L3 switches do not support NAT so you may be out of luck unless you can insert a firewall/router in between.

Jon

[de fl]

Its a WS-C4900M running cat4500e-ipbase-mz.122-46

[Jon Marshall · Accepted solution]

Unfortunately that switch doesn't support NAT.

So unless you can insert a device that can between the clients and server you are not going to be able to do it, at least from a network perspective.

Jon

[Karsten Iwen]

Your plan is using the wrong tool for this tasks. For SMTP (TCP/25) authentication is optional and the mail-server could be configured to accept mails based on the source address of the two network-devices. But for submission (TCP/587) there MUST be an authentication (thats mandated by the RFC 4409). So you will also end up with the need to authenticate.

Have you also checked if you can upgrade the devices? Perhaps a newer software is capable of smtp-auth.