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I have a client that was recently acquired by a company. Their email system now resides on the parent company's network. Currently there is no VPN setup between my client and the parent company.

I need to setup an SMTP server locally to deliver email to the parent company's SMTP server. Currently I have a WIndows Server 2008 R2 running the SMTP feature (IIS 6.0). Under the Virtual SMTP Server, I have setup the domains for the parent company and my client. The parent company has a direct link to their mail server at, whereas going to will result in some spam filtering.

Obviously I could go into the Virtual SMTP server and set the Outbound delivery port to 587 and set the smarthost for the entire virtual SMTP server to go to the parent company. However, we only want emails going to the local domains to go through the parent company's SMTP server and we would rather send all other domains out through the local SMTP server.

Next step was to setup remote domains in the Virtual SMTP server, but when I choose to send the email for the specific domains through a smarthost, I cannot specify a port.

Does anybody know a way around this without forcing all email out port 587?


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If you can configure an additional IP address for this machine, you can use the following solution:

  1. Create a new Virtual SMTP server that will listen on the new IP address under port :25, but will have Outbound Delivery Port set up to :587
  2. Configure the existing Virtual SMTP server to forward the mail for parent company to the new Virtual SMTP server
  3. Configure the new Virtual SMTP Server to forward mail to parent company's server

If you can't configure an additional IP address for this machine, you can set up a new Virtual SMTP Server on another machine.

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