Mail sent successfully but failed to be received

I tried to send mail to personal email

me@host:~$ mail -s "Sending a Tesing"
Cc:
This is a testing mail.

The records :

me@host:~$ tail -n 15 /var/spool/mail/gaowei | sed "s/$USER/me/g"
Subject: Sending a Tesing
To: <>
Cc: <>
X-Mailer: mail (GNU Mailutils 3.4)
Message-Id: <20190317063817.D05E5600B53@alpha>
Date: Sun, 17 Mar 2019 14:38:17 +0800 (CST)
From: me <me@host>
This is a testing mail.
--D05E5600B53.1552804699/host--

It seems that my email has been sent successfully.

Unfortunately , gmail does not receive such an email either in junk box.

What's the problem with my usage of mail?

Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.