551 User not local; please try

Recent two weeks my website’s email system has a lot of emails returned. And the error messages are exactly the same.

The error message is

“551 User not local; please try <forward-path>”

All emails returned have same characters: The recipients’ email servers are located in China. sina, yahoo.cn, 163, and sohu, no exceptions.

I did some googling and found out this has something to do with China’s Great Fire Wall. 10.1 is a special day in China. The fire wall might have been tightened.

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