I have a micro-device that is capable of sending out emails via an SMPT Client. However, the device does not have a DNS Client, so the only way to send out email is to specify the IP Address of the SMTP Relay instead of the domain name.

For example: When the device sends out an email, it will initialize its SMTP Client that looks something like:

SmtpServer =;
Port = 343;
From: so@stacko.com

Unfortunately, we are not able to initialize the SMTP Client using the domain name of the relay with something like:

SmtpServer = relay.smtp.com;
Port = 343;
From: so@stacko.com

I've tried my best to get our micro-device developer to support a DNS Client, to not avail. So, we are stuck with the device using an IP to specify the SMTP Relay server.

We were originally planning on using a third-party for the SMTP service, but now that we have this problem of no DNS support, we cannot go the third-part route because we cannot trust that their IP Address will remain static. Most likely, their IP Address will change monthly, weekly, or maybe even daily.

With that as the background to my problem, my question is - Is there some type of router that can detect an incoming email request and then forward that request to a remote SMTP Server?

Summarizing the two problems:

  1. We don't want to manager our own SMTP Server and would prefer to pay a third-party service to do that for us.
  2. Since the micro-device cannot support a DNS client, it must point to an IP Address that we have complete control and knowledge of (we cannot trust what third-party services will do with their IP's).

To solve the two problems noted above, I'm thinking that I would configure a device that I have complete knowledge and control of its public IP Address. This device/router is what the embedded-device will send its emails to. Then the device/router will forward the email to a third-party SMTP service via the domain name of that SMTP Server (not the IP Address of the SMTP Server).

In a nutshell: The micro-device sends email via IP Address to fancy-router-thing which forwards the email via domain name to third-party-SMPT-guy.

Do you know of a router (or any non-SMTP server device) out there that can detect an incoming SMTP packet and forward it to a remote SMTP Server?

Or - do you have any ideas/suggestions what I can do to work around the two problems I mentioned above (other than get medieval on our micro-device dev'er..ha!)?


Why don't you just run an SMTP server that subsequently uses a third-party relay?

micro device -> smtp delivery -> your relay -> smtp delivery -> third party relay server

SMTP is designed to go through multiple hops, plenty of e-mail that leaves businesses go through an internet facing SMTP relay that itself uses an ISP based SMTP relay.

  • I considered doing that, but I thought it would be easier and cheaper to go with a router - assuming that a router exists that can do what I'm trying to do. – Jed Aug 29 '11 at 21:44
  • Maybe, but SMTP is designed to hop through servers, it takes literally 1 minute to setup postfix or exim4 in a smart relay config which only relays for certain inbound addresses and it's just works. Standard, simple and most importantly, standard. – EightBitTony Aug 29 '11 at 22:59

SMTP is a simple TCP protocol, depending on how your network is setup you could possibly just create a NAT rule to forward traffic to your real server, or perhaps setup a TCP proxy with something like netcat, tcproxy, or one of many similar tools.

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