This error is usually caused by your MTA (possibly postfix) writing the recipient email address during the rcpt to stage of sending the letter to the other party's MTA. It is possible that the recipient of the letter you sent does not exist. . The anti-spam strategy of QQ mailbox is not excluded
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This error is usually caused by your MTA (possibly postfix) writing the recipient email address during the rcpt to stage of sending the letter to the other party's MTA. It is possible that the recipient of the letter you sent does not exist. . The anti-spam strategy of QQ mailbox is not excluded