Problem

Email cannot be delivered to your server

Causes and Resolutions

There are many potential causes of this problem.  Try the steps below, in order, to identify the root cause of the problem.

Cause 1 - Incorrect / Unpropogated MX records

The first things to test are the MX records for a domain for which you can't receive email.  To get the MX records for your domain, go to a command prompt and type the following:

• nslookup
• set type=MX

Enter in a domain that is hosted by your server.  You will receive a response similar to this:

Server:  <Your primary DNS server>
Address:  <IPAddress>:53

example.com        MX preference = 10, mail exchanger = mail.example.com

mail.example.com   internet address = 123.123.123.123

When an external mail server makes an SMTP connection, it will utilize the MX record that it resolves. In this case it would be: 123.123.123.123.  Please verify that the domain’s MX record is pointing to correct IP for the hosted domain on the server.

Cause 2 - Server not listening on port 25

If your MX records are setup correctly, please verify that the server is listening on port 25.  This can be accomplished by entering the below command at a Command Prompt window:

• telnet <IP Address> 25

When you do this you will receive a response like this:

220 mail.example.com

Type ‘quit’ to end the session. If any other 220 response is received or a 220 response is not received at all, the email service is not listening on port 25.

If you get no response when you telnet to your mail server there are a couple possible reasons.  One might be the computer that you are trying to connect from.  Many ISP's block outgoing connections to port 25.  Try to telnet to your mail service from a command prompt on your actual server.  If you can't connect from your home or work computer but can connect from your actual server, then a firewall is blocking connections to your mail server.

If you get no connection when you telnet to your mail server from a command prompt on your mail server, then the mail service either isn't listening on port 25 or a software firewall is preventing any connections to it.  To see if something is listening on port 25, go to a command prompt on your server and type:

• netstat -a -n -p tcp

You will get a listing of TCP connections on your server.  When something is listening on port 25 on 192.168.0.1 (for example) you will see this line:

TCP     192.168.0.1:25     0.0.0.0:0     LISTENING

Look for anything listening on port 25 of the IP that the mail server should be listening on.  

Cause 3 - SmarterMail cannot obtain port

If your domains MX records are setup correctly and the domain is using the correct IP, but nothing is listening for SMTP traffic on that IP try restarting the mail service.  It is possible another program may have prevented the mail server from listening on that IP in which case you would need to restart the service to get it to listen on that IP again.

Cause 4 - Something else