I've tried using my SMTP2Go and Gmail accounts and it seems that after I installed this router, I stopped being able to send out emails using IIS's Virtual SMTP server. I've tried ports 25, 587 and 2525 using TLS and each time the message gets to the "AUTH" stage according to the logs, but never continues. Then 5 minutes later when the server tries to resend that message it repeats the process. I never get any errors in the logs - the process seems to just stop. Looking at logs before the swap I see several actions happening after the "AUTH" procedure but they don't happen with this new router. I have to assume it's the firewall.

I'm a computer guy but not a "router" guy per-se. I thought I setup an Access Control entry for the IP of the server to Allow all activity outbound, but that didn't seem to fix it. 

I've configured IIS's Virtual SMTP server according to SMTP2Go's instructions so I'm convinced I've got that part right because it looks like all the details are there. There's so little in TP-Link's information I'm struggling here.

I CAN send emails using Outlook Express from this server using the same settings for ports and server. I can see that SMTP2Go recognizes me, because I get a "Hello" message in the logs and even a "TLS Go Ahead" message...

Don Hancock