Testing an external mail server

There are times when I need to test the basic functionality of an external mail server (i.e. one I don’t control). Here’s a step-by-step process to perform some basic testing using telnet:

1. Telnet to the remote server:
   telnet <server> 25
   If it replies, you should get a response like:
   Trying <server>...
Connected to <FQDN>.
Escape character is '^]'.
220 <FQDN> ESMTP
2. Announce your domain to the remote mail server:
   helo <myDomain>.com
   The reply should be:
   250 <server>
3. Specify my email address to the remote server:
   mail from:<emailAddress>
   Should result in the reply:
   250 sender <emailAddress> ok
4. Specify the intended recipient:
   rcpt to:<emailAddress>
   The server responds with:
   250 recipient <emailAddress> ok

If you get 220/250 responses across the board then this is a reasonable indicator that the mail server is performing properly.