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:
- Telnet to the remote server:
telnet <server> 25
If it replies, you should get a response like:
Connected to <FQDN>.
Escape character is '^]'.
220 <FQDN> ESMTP
- Announce your domain to the remote mail server:
The reply should be:
- Specify my email address to the remote server:
Should result in the reply:
250 sender <emailAddress> ok
- Specify the intended recipient:
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.