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.

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