Your email server was unable to be sent because your mail server rejected the message 550 5.7.1. client does not have permission to send as this sender. 1003, 10.

Hello All,

User is creating a code where it executes and sends two emails from our company portal 1. To the user and 2. To the approver / user's manager. However it was working fine before and after period of time it stopped now and it gives an error message as below :-

"Your email server was unable to be sent because your mail server rejected the message 550 5.7.1.
cleint does not have permission to send as this sender. 1003, 10."

Please advice !!!