如果电子邮件不存在，函数返回错误的。

If the E-mail does not exist, function returns false.

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函数返回错误代码或成功代码；如果是错误代码，则代码本身可用于指出何处出错。

The function returns an error or success code; if it's an error code, the code itself can be used to figure out what went wrong.

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当互斥被锁定或者发生错误时，函数返回。

The function returns when the mutex is locked, or if an error occurred.

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