Tool Time: Test Connectivity to Remote Email Servers with TestMX

One command is all it takes to check connections

It’s probably happened to you at some point: Users are unable to email people at a specific domain. As the administrator, it’s your job to find and solve the problem.

As you divide and conquer your way to a solution, you’ll no doubt want to try to “manually” connect to the destination email server. You can accomplish this by using Telnet to connect to port 25 of the destination server. To find that server’s host name, you can use a command-line utility such as Nslookup or a web-based DNS tool such as the one at However, there’s an easier way to quickly determine whether your email server can connect to the destination server: Use TestMX.

You can download TestMX from After doing so, copy testmx.exe to the root of the C drive on your email server. Installing it on an email server rather than a PC prevents problems with firewalls and reverse lookups and ensures that you’re comparing apples to apples.

To use TestMX, open up a command prompt and type:

testmx –dDomain

where Domain is the name of the domain that you want to test. Note that there should be no space between the –d and the domain name. TestMX then takes care of finding and connecting to the email servers in that domain.

That’s it! In just a few short seconds, you can use TestMX to confirm connectivity to the remote email server. With this information, you can then move to the next step in your troubleshooting process.

—Eric B. Rux, senior
Windows administrator
and cofounder of

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