To test SMTP from the command line:

1. telnet host-to-test 25 (connect to port 25 on mail server)
2. HELO sending-host
3. MAIL FROM: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
4. RCPT TO: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
5. DATA
   (enter one blank line after DATA)
6. Subject: test
   To: to-user
   From: from-user
   (enter one blank line after From:) test text for email
   . (enter a single period by itself on the last line)
7. QUIT

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To test SMTP with SMTP AUTH (no TLS/SSL) from the command line:

First, use a perl script to compute the Base64 encoded user ID and password needed to authenticate to the mail server. This requires the MIME::Base64 module.
perl -MMIME::Base64 -e 'print encode_base64("\000userid\000password")'

The output looks something like this:
AHVzZXJpZABwYXNzd29yZA==
Copy the output string so it can be pasted into the AUTH step below.

1. telnet host-to-test 25 (connect to port 25 on mail server)
2. HELO sending-host
3. AUTH PLAIN Base64-encoded ID/password
4. MAIL FROM: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
5. RCPT TO: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
6. DATA
   (enter one blank line after DATA)
7. Subject: test
   To: to-user
   From: from-user
   (enter one blank line after From:) test text for email
   . (enter a single period by itself on the last line)
8. QUIT