https://www.ndchost.com/wiki/mail/test-smtp-auth-telnet

https://www.ndchost.com/wiki/mail/test-smtp-auth-telnet

perl -MMIME::Base64 -e ‘print encode_base64(“username”);’
perl -MMIME::Base64 -e ‘print encode_base64(“password”);’

user@localhost[~]# telnet exampledomain.com 25
Trying 1.1.1.1…
Connected to exampledomain.com (1.1.1.1).
Escape character is ‘^]’.
220-server1.exampledomain.com ESMTP Exim 4.66 #1 Wed, 09 May 2007 23:55:12 +0200
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
EHLO exampledomain.com
250-server1.exampledomain.com Hello  [1.1.1.2]
250-SIZE 52428800
250-PIPELINING
250-AUTH PLAIN LOGIN
250-STARTTLS
250 HELP
AUTH LOGIN
334 VXNlcm5hbWU6
dXNlcm5hbWUuY29t
334 UGFzc3dvcmQ6
bXlwYXNzd29yZA==
 
235 Authentication succeeded

https://www.ndchost.com/wiki/mail/test-smtp-auth-telnet