How to mail server responses telnet command!

[zibra]

I wonder how does mail server response a telnet command?
1. when I telnet to the first mail server, (example: "# telnet mail.abc.com 25"), mail server reply:
220 mail.abc.com ESMTP Postfix

and I can use some commands of telnet to send mail.

2. when I telnet to the second mail server, (example: "#telnet mail.xyz.com 25"): mail server reply:
220 ********************************

and I can't use any commands from telnet to send mail.

Please help me to distinguish these two cases.

These two mail servers are the same and are zimbra mail server.
Many thanks,