Question: SMTP not sending mail

I received quite a number of questions from time to time. Rather than replying via email (which I don't normally do it), I will pick a few and blog it here :) So here we go:

Question:
Sent From: ptjoe
Subject: SMTP not sending mail
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I saw one of ur replies in the IIS forum about an smtp problem.
It happens taht i have the same problem, i have the smtp installed on IIS 6.0, i set up an account in outlook express with that smtp server. when i send a msg on outlook apparentely it sends the message, but the message never gets to it's destination, and i noticed that the message remains in the queue folder on the mailroot. Can you tell me what may be causing this ?
thank u in advance.

Answer:
Well, for starter, I would suggest you try this blog post - Troubleshooting IIS SMTP, basically, you will check if the smtp component can make connection out via tcp port 25 + the udp/tcp 53 for DNS MX queries. If you pass both yet the message stuck in the queue, then you need to look at the smtp log. Find out the exact error status code, etc. Typically, if you have a fresh smtp box and try to send/relay mail to mail host like hotmail.com, yahoo.com, gmail.com etc. You need to make sure that your smtp server is clean. Not blacklisted, have a valid reverse-lookup DNS name record, etc. Here's a good URL (http://www.dnsreport.com/) to check your DNS records and provide information on how you should deal with each warning or error message.