When troubleshooting email, one tool I use again and again is my trusty telnet client. With that one simple command line tool, and a little knowledge of the RFCs, I can usually debug network issues related to email delivery, or at least narrow them down quickly without resorting to packet captures, reconfiguring clients, or other legerdemain. While most old school colleagues will go to telnet without a second thought, many others seem to think this is eldritch magick, so today we are going to learn how to use telnet to test SMTP.

One reason many of the newer IT professionals may not be as comfortable with telnet is because it is not included be default in the newer Microsoft operating systems. Starting with Vista, Microsoft decided to make you ‘opt in’ to using it, probably because it does transmit all traffic in the clear, and as such, could expose passwords or other confidential information. While that is true, and a very important thing to understand, using it to connect to services, grab banners, and send simple mail is safe enough, and I keep a generic account handy for things that require logins so that I can test without exposing my true domain account credentials. Here’s how to get started.

Continue reading Using telnet to test your mail server

An essential skill for email administrators is being able to dive into the command line to troubleshoot email delivery and connectivity problems.  In this post I will explain some of the simple command line techniques you can use for diagnosing these email issues.

NSLookup

NSLookup is the command line utility for querying the Domain Name System (DNS).  Because email delivery relies so heavily on the Mail Exchanger (MX) records contained within DNS you need to know how to use it for verifying DNS configurations.

When someone reports a problem sending email to an outside party and you want to investigate it one of the first things you’ll need to determine is the name or IP address of their mail server.  This is the job of the MX record, which you can query using NSLookup. Continue reading Diagnosing Email Server Problems with the Windows Command Line