Is there an SMTP Relay Server?

Is there a package that acts as an SMTP relay server to use for sending mail from another machine to the OpenWRT router to then be delivered to a smarthost? Apparently most of these are only for sending localhost mail which is useless for me.

Run postfix on hardware designed for constant disk activity (flash is not) and sufficient RAM. Port-forward smtp and submission to it.

The security risks alone of running a mail server should be reason enough not to run it on your perimeter firewall.

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I agree with @jeff, Postfix can be ran as a relay; but I don't suggest on your router. Fruther, if you have a residential-block IP address from your ISP, the mail will likely be rejected by most well known and established email companies. It's also possible your ISP simply blocks it.

You can run Netalyzr to verify your ability to send mail on port 25/tcp.

http://netalyzr.icsi.berkeley.edu

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I can't figure out how to enable SSL auth on postfix which is what I'm using currently not on the router.

I just need something simple to relay IoT and PHP notifications to my host Yandex which has some pretty strict requirements for sent mail compared to Comcast.

Yes my ISP blocks 25 so I'm not concerned about external spam.

No, emails don't get marked as spam as long as you are using your own email domain and configure the DNS records correctly.

Comcast here blocks 25 entirely (src/dst) so sending mail is blocked as well, or probably as the primary intent.

I run a closed “smart hub” on a server at DigitalOcean as a result. I can help you with the Postfix config, but you’ll need to determine if you can connect to port 25, or you won’t be able to send mail to outside destinations directly from your local hosts.

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You're not concerned about actually sending email once you setup your server, either.

This is the port used to transmit email. You'll need a new ISP, or an upgrade to a business account.

Also, your reasoning for why email is flagged as spam is quite lacking. Lastly, I never mentioned spam. I said they would reject the emails from residential IPs.

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This comes late, but the package https://openwrt.org/packages/pkgdata/emailrelay may do you want.

Here is the manual: http://emailrelay.sourceforge.net/

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I think what the original poster wanted is SSH local port forwarding to using SSH encrypt plain text email into SSL email, so that it can be send through whatever email server, as long as it has account on that server.

SSH local port forwarding can be done on regular Linux computer, but not sure if OpenWRT support that?

That might be a job for stunnel. Openwrt has a package for stunnel, but I have never succeeded in configuring it.

You are right. I was able to create a stunnel on regular Linux box. But could not find how to do this on router.

I created a wiki page for the E-Mail Relay:

Please check