SEND MAIL: ERROR CODE 550

SEND MAIL: ERROR CODE 550

I have a problem since 2 days: i can not send email from ZOHO.
Please help me, it is very very important.

This is the error i get:

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.

 

dohuuhoan@omega-engineering.vn, 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. r184si19601242pgr.266 - gsmtp

 

nguyenthanhchung@omega-engineering.vn, 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. r184si19601242pgr.266 - gsmtp

 

trinhthinhung@omega-engineering.vn, 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. r184si19601242pgr.266 - gsmtp

 

 

 

 Received:from NGOCNV (123.24.241.91 [123.24.241.91]) by mx.zohomail.com

               with SMTPS id 1550716503530277.72804172885265; Wed, 20 Feb 2019 18:35:03 -0800 (PST)  Message-ID:<!&!AAAAAAAAAAAYAAAAAAAAAOs3qzFUPMFCifyNVzY7W0jCgAAAEAAAACAW3vrYH5xNqYFLCoThyLUBAAAAAA==@bkaii.com.vn>

 Date:Thu, 21 Feb 2019 09:35:00 +0700

 From:Nguyễn Văn Ngọc <ngocnv@bkaii.com.vn>  To:"'Chung Nguyen Thanh'" <nguyenthanhchung@omega-engineering.vn>

 Cc:"'Hoan Do Huu'" <dohuuhoan@omega-engineering.vn>,

               "'nhung trinh thi'" <trinhthinhung@omega-engineering.vn>

 Subject:RE: XIN BÁO GIÁ HỆ THỐNG TÍN HIỆU GIAO THÔNG  Content-Type:multipart/related;

               boundary="----=_NextPart_000_000E_01D4C9C8.B8C22380"