Is it possible to verify whether a mailbox exists?

Is it possible to verify whether a mailbox exists? Because mailbox verification has not been enabled before, there are many invalid mailboxes in the user information. now we need to mark the users in the mailbox. Whether the mailbox format is correct or not, whether the mailbox domain exists can also be confirmed by sending a communication via socket, and whether the mailbox exists. how can this problem be solved? Solve ., I have written SMTP and used it to filter 1 million email addresses. many of them are outside China. Is it possible to verify whether a mailbox exists?
Because mailbox verification has not been enabled before, there are many invalid mailboxes in the user information. now we need to mark the users in the mailbox.
Whether the mailbox format is correct or not, whether the mailbox domain exists can also be confirmed by sending a communication via socket, and whether the mailbox exists. how can this problem be solved?
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SMTP
I wrote that filter 1 million email addresses, many of which are foreign
There were also many problems during the period, some of which were unstable. the first time I returned a second time, the second time I returned a non-existent result, and I was also depressed.
For security reasons, it seems that anonymity is not working now.
This is the general implementation process. you must refer to the SMTP protocol description.
See an article I wrote

Http://blog.csdn.net/franzhong/article/details/6311654