[root@linuxserver01 ~]# telnet smtpserver01.contoso.com 25
Trying 10.0.1.2...
Connected to smtpserver01.contoso.com.
Escape character is '^]'.
220 smtpserver01 Microsoft ESMTP MAIL Service, Version: 10.0.14393.0 ready at Tue, 27 Nov 2018 11:03:33 +0900
helo smtpserver01.contoso.com
250 smtpserver01 Hello [10.0.1.2]
mail from: user01@contoso.com
250 2.1.0 user01@contoso.com....Sender OK
rcpt to: user99@example.com
250 2.1.5 user99@example.com
data
354 Start mail input; end with <CRLF>.<CRLF>
.
250 2.6.0 <SMTPSERVER01nHM3SOl00000006@smtpserver01> Queued mail for delivery
quit
221 2.0.0 smtpserver01 Service closing transmission channel
Connection closed by foreign host.