SMTP Error: timeout exceeded

Issue

• telnet to email server shows Error: timeout exceeded.

# telnet localhost smtp
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 smtp.example.com ESMTP Postfix
421 4.4.2 smtp.example.com Error: timeout exceeded << == showed message
Connection closed by foreign host.

And then maillog

Month day 02:08:07 hostname postfix/smtpd[PID]: connect from localhost[::1]
Month day 02:08:37 hostname postfix/smtpd[PID]: timeout after CONNECT from localhost[::1]
Month day 02:08:37 hostname postfix/smtpd[PID]: disconnect from localhost[::1] commands=0/0