SMTP Relay

525 pts.
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Microsoft Windows Server 2003
SMTP Relay
I am looking to set up an SMTP relay for a particular situation, but the exact configuration is not quite right. In my server room, I have an internal network used for (among other things) connecting up the various servers to the backup server which is normally not externally open (except for updates), cluster heartbeat, etc. One of the devices on my internal-only network is an APC network management card. It has the option to send email notifications out, however since it is on the 192.168.0.x internal only network, it cannot directly reach any SMTP or Exchange servers. Several of the servers on the internal-only network also have a NIC that connects externally, so it seems my logical option would be to set up an SMTP relay on one of them, to forward emails from the internal network out to my SMTP or Exchange server IP. However, I have played around with the SMTP relay application after installing it, and I am not sure exactly how to do it. The instructions I used were from MS TechNet, as the 'spare' server I am testing this with is Server 2003 Standard R2. Assuming the NMC is 192.168.0.100, and the IP of my external SMTP server is 10.10.10.1 (example), and the server in between has both 192.168.0.101 and 10.10.10.2 as its NICs, how exactly would I set this up? Again, the instructions on TechNet were followed, but it seems like they're more concerned with forwarding emails INTO the internal network.

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Traffic has to be routable from one network to the other. This means that there must be some device with both a 10.x.x.x and a 192.168.x.x. address. This device must have routing enabled between the networks to pass traffic between the networks. Traffic flow will be bidirectional since SMTP uses TCP and there are acknowledgement and control messages sent back and forth between the hosts involved in the transaction. If the server in question has both addresses on a single NIC, the SMTP service must be configured to listen on the same network as the sending SMTP host. You can test this by running a telnet session to port 25 on that host to see if the SMTP service answers.

–Reply from LoneWolfBW

The issue turned out not to be that (per my post, I had the SMTP relay installed on a server with two NICs, one on each network).

I had set up the SMTP relay to forward to the IP address of our SMTP server. That was what was failing per below.

I changed the setting to the FQDN of the SMTP server and that works.

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  • Technochic
    It would be helpful to know what steps you have followed so we don;t suggest what you have already done. Please be specific about "instructions on TechNet were followed". What was followed? Thanks?
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  • Lonewolfbw
    Sure, here's the instructions I followed, verbatim: -------------------------------------------------------------------------------- To configure a Windows Server 2003 server as a relay server or smart host In Internet Services Manager, add the SMTP mail domain for which you want the Windows server to relay. To add the SMTP domain: Click Start, point to Programs, point to Administrative Tools, and then click Internet Services Manager. Expand the server that you want, and then expand the default SMTP virtual server. By default, the default SMTP virtual server has a local domain with the fully qualified domain name (FQDN) for the server. To create the inbound SMTP mail domain, right-click Domains, point to New, and then click Domain. In New SMTP Domain Wizard, click Remote as the domain type, and then click Next. In Name, type the domain name of your SMTP mail domain for your Exchange organization. Click Finish. Configure the SMTP mail domain that you just created for relay: In Internet Services Manager, right-click the SMTP mail domain, and then click Properties. Click Allow the Incoming mail to be Relayed to this Domain. Click Forward all e-mail to smart host, and then type the IP address in square brackets ([ ]) or the FQDN of the Exchange server that is responsible for receiving e-mail for the domain. For example, to enter an IP address, type 123.123.123.123. Click OK. Specify the hosts that you want to openly relay to all domains: In Internet Services Manager, right-click Default Virtual Server and click Properties. On the Access tab, click Relay. Click Only the list below, click Add, and then add the hosts that you want to use the SMTP server to send mail. Under Single computer, specify the IP address of the Exchange bridgehead server that you want to relay using this SMTP server. Click DNS Lookup to find the IP address of the specific server. -------------------------------------------------------------------------------- Following these instructions, I ended up with a default domain of servername.domain.edu, which is the FQDN of that server itself (which is as it should be). I then added a new SMTP domain, using the setting "Allow Incoming mail to be relayed to this domain", I selected "Forward all mail to smart host" and put in the IP address of the public SMTP server we use. However, attempts to forward mail out fail. I kept all other defaults.
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  • Lonewolfbw
    I have found the solution: Per above, I had set up the SMTP relay to forward to the IP address of our SMTP server. The emails, however, would still not route out of the internal network and through the relay to the server. Once I changed the setting to the FQDN of the SMTP server, however, the SMTP relay began working and I can now email from the device on the internal network, out to our mail server and on to the world. Thanks for all your replies, everyone.
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  • Labnuke99
    Thanks for the feedback. Interesting that the ip address would not work.
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