I've been trying to figure this out for a couple days now. I've got a little linux box that should send email alerts and I need to test this functionality. It's a very, very basic linux box (painfully so).
Is it possible to setup a fake SMTP server on my desktop (IP:192.168.0.20) that it (192.168.0.2) can send emails to? I need to confirm that the messages are correct in content, but that's all. I'm perfectly fine having this spit out to the terminal. There's no DNS on the local network, or DHCP, I'm just using static IP addresses so it needs to work within that limitation.
I've been able to confirm with wireshark that the embedded computer is trying to do something over SMTP, but I don't see any message content at all, looks like it's just trying to talk to the server. I've also tried sending a message using "mail" but I keep getting an "SMTPclient: agent: unknown host" error, which I assume means it can't find the SMTP server I'm telling it to find.
I'm using Ubuntu 14.04 on my desktop.
Thanks!
So, as a basic test it works to just have an SMTP server running on your local machine. Installing Postfix should be all that's required. I set up the relay to our local mailserver but it wouldn't relay through. From the error messages I was getting I gather this is a DNS issue, it can't resolve where to direct the message. Watching wireshark you should be able to see the traffic and the attempt to send the message, which is something I guess. I will update when I have a better answer.