SMTP Error: The following recipients failed

Describe the problems I encountered:
After receiving phpmailer, The following Error was reported: SMTP Error: The following Error was received: XXXX Server Error: ‘4.7.1 < mail address sending to> Relay access denied’
I put the code in the same room with SMTP server on the machine can normal to send, after the change back to ali cloud is an error, I am depressed, Google once met this question a lot, but haven’t been able to solve my problem, and then I try to modify the inside of the phpmailer configuration, after changing the SMTPAuth to true unexpectedly send mail properly, the original is useless authentication out of wrong, but I in another machine SMTPAuth is false is normal, don’t know the reason why is it the same room so no authentication is required

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