Error code 550 - I can't send my email to gmail

Error code 550 - I can't send my email to gmail

I have this problem with all my user email.
But when they send the email again, email can send.

What can i do to remove this problem?

Please contact me throw
hoangtucse@gmail.com
hoangtu@chuonchuonkim.edu.vn

---------------------------
This message was created automatically by mail delivery software. 
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.  

vegefoods58@gmail.com, ERROR_CODE :550, ERROR_CODE :5.7.1 This message does not have authentication information or fails to pass 
            5.7.1 authentication checks. To best protect our users from spam, the 
            5.7.1 message has been blocked. Please visit 
            5.7.1  https://support.google.com/mail/answer/81126#authentication for more 
            5.7.1 information. a37si2552007edd.321 - gsmtp 



Received:from ACERPC (14.161.5.165 [14.161.5.165]) by mx.zohomail.com 
    with SMTPS id 15504780585741012.7784696652514; Mon, 18 Feb 2019 00:20:58 -0800 (PST) 
Message-ID:<002901d4c762$d9488d00$8bd9a700$@chuonchuonkim.edu.vn> 
Date:Mon, 18 Feb 2019 15:20:43 +0700