There are many potential reasons that a mail server does not properly receive mail. This article identifies the most common causes of failed inbound email delivery, and some possible resolutions for these issues.

Incorrect/unpropagated MX records
The first things to test are the MX records for a domain for which you can't receive email. Bad MX records in DNS result in remote email servers not knowing which IP address should receive the 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 installation of SmarterMail. You will receive a response similar to this:

Server:
Address: :53

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

mail.example.com internet address = xxx.xxx.xxx.xxx

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

SmarterMail not listening on port 25
If your MX records are setup correctly, verify that SmarterMail is listening on port 25 of your mail server. This can be accomplished by entering the below command at a Command Prompt window:

telnet 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 SmarterMail 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 SmarterMail server from a command prompt on your SmarterMail server. If you can't connect from your home or work computer but can connect from your SmarterMail server, then a firewall (likely your ISP's 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 SmarterMail 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 SmarterMail server and type:

netstat -abnp 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 SmarterMail should be listening on. If this isn't there, then it is likely that SmarterMail has not been setup to listen on the correct IP. The IP addresses and ports that SmarterMail will listen on are configured on the "Settings->Bindings->IP Addresses" and "Settings->Bindings->Ports" pages.

SmarterMail cannot obtain port
If your domains MX records are setup correctly and the domain is using the correct IP, but nothing listening for SMTP traffic on that IP try restarting the SmarterMail service. It is possible another program may have prevented SmarterMail from listening on that IP in which case you would need to restart the SmarterMail service to get SmarterMail to listen on that IP again.

Something else
If you are still unable to receive mail at this point, please contact SmarterTools support.

All other settings are optional. For more information on domain throttling, please refer to the SmarterMail Online Help.