telnet 192.168.111.24 25
Connected to et24 (192.168.111.24).
Escape character is '^]'.
220 mail.embeddedteam.co m ESMTP Postfix
250 mail.embeddedteam.co m
354 End data with
250 Ok: queued as 2D40A7D29
There are many options with this type of checking
You can give ehlo instead of helo and the system will show all authentication available.