Not sure what you mean, but if you mean "telnet mailhost 25"
than here is an example: telnet mail.xxx.xxx 25
Connected to mail.xxx.xxx.
Escape character is '^]'.
220 mail.xxx.xxx ESMTP helo HOSTNAME
250 xxx.xxx mail from: sps@localhost
250 ok rcpt to: email@example.com
250 ok data
354 go ahead From: sps@localhost
THis is a test
250 ok 1000313764 qp 29803 quit
Connection closed by foreign host.
Note that the respone from the server may vary (this is talking with qmail).
Hope This Helps,