How to add an SMTP carrier

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SMTP configurations vary from network to network. Some networks allow direct SMTP over port 25, others require that you relay your messages through a mail server.


To determine which variety of SMTP is available to you, there is a connection test you'll need to run that requires the Telnet Client to be enabled in Windows.


If you use Windows XP or Server 2003, the Telnet Client is enabled by default. If you use Windows Vista, 7, 8/8.1, Server 2008 or Server 2012, you will need to enable the Telnet Client.


For information on how to enable the Telnet Client in Windows Vista, 7 or Windows 8/8.1, click here.


For information how to enable the Telnet Client in Server 2008 or Server 2012, click here.


After the telnet client has been enabled, this is the port test you'll want to run:


1) In Windows, run a Command Prompt.


2) In the Command Prompt, type the following and hit enter:


telnet 25


If port 25 is open and there are no outstanding issues with the public IP address the system sits behind, you'll receive a 220 response.

If you receive a 220 response, use the Adding a direct SMTP Carrier steps.


If port 25 is open but there is an outstanding issue with the public IP the system sits behind, you'll receive a 554 or a 421 rejection notice.

This indicates that your public IP is on a blacklist, so you will need to determine which blacklists you're on. To do that, from the computer running the software, go to and get your public IP. Then click on the Blacklist Check option at the top of the page and run the test. Any list that has a red ! next to it is a list the IP address is on, so you'll want to go to each of those links and go through their provided lookup and removal steps. Once your IP is off of those blacklists, you can use direct SMTP from that system.


If port 25 isn't open at all, you'll receive a response that says "Unable to establish a connection to the host on port 25".


If port 25 isn't open, you may be able to have it opened but you will need to speak with your network administrator or internet service provider's tech support.


If port 25 is closed and cannot be opened, you must relay your traffic through an SMTP server and you will need to contact your local IT staff or internet service provider's tech support and ask them the following questions:


1) What SMTP Server can you use?


2) What port should you connect to that server on?


3) Does that server require authentication?


3a) If the server does require authentication, what styles of authentication are supported and what username and password should you use to authenticate with?


Once you have the answers to those questions, use the Adding a relayed SMTP Carrier steps.