We all know how to test SMTP server by telneting to port 25. But, what if you have to test a SMTP server that has to be authenticated before you send a test mail using telnet. The only difference from normal test is, here you have to authenticate with the user/password, not in plain text, but you should send the authentication string with a Base64-encoded (http://base64-encoder-online.waraxe.us) password.
So, here is how you would test authenticated smtp server using telnet.
telnet smtp.mymailserver.net 25 220 mi1 ESMTP service ready ehlo localhost 250-mi1 250-8BITMIME 250-SIZE 20480000 250-AUTH=PLAIN LOGIN 250-AUTH PLAIN LOGIN 250 STARTTLS Auth Login 334 VXNlcm5hbWU6 c3VwcG9ydEyMHBsdXNjbHViLmNvbQ== 334 UGFzc3dvcmQ6 RHZsNIwWA== 235 Authentication successful. MAIL FROM: email@example.com 250 Sender address accepted RCPT TO: firstname.lastname@example.org 250 Recipient address accepted DATA 354 Continue This is a test message for SMTP auth using telnet. Plz ignore. Don't reply. . 250 Delivery in progress
So, the difference is what you see in those 3 lines starting from “Auth Login” and the following 2 codes are username and password respectively which does SMTP authentication. Those 2 encoded codes are generated using http://base64-encoder-online.waraxe.us
I hope this helps.