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How do I find out if an email address is invalid?

My email address at www.email.it is disabled because I have not used it for a long time.

Now when I go to FB, I get this message:

"Our systems have detected that xxxxxxx@email.it is no longer a valid email. "

So my question is:

How can these systems detect that the letter is valid?

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6 answers

You cannot determine if the email is fake. All you can do is determine if the RFC 5322 string matches the actual format of the email address. You cannot know if such an account was advertised on the target SMTP server if you do not own this server. You can probably try to send an email to this address and see what the remote SMTP server will reply.

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You cannot reliably determine whether the letter is valid or not. SMTP servers intend to implement the VRFY command, but many of them are disabled so that spammers cannot find a valid email address.

In addition, even if the email address matches the correct email address of RFC 5322, this does not mean that it is a valid email address on the target server; many servers do not properly implement this standard!

The best thing you can do is send an email to your feedback email address. If the email address is valid and the user reads the email and the user clicks on the link, then it may happen that the email address is valid (it could be intercepted, which would give you a false positive).

If the email bounces back, this may indicate that the email address is invalid (but it may also be that the target server is down, or the mailbox is full, or who knows what else).

As you can see, SMTP is extremely unreliable given how well it works in practice.

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Most likely, Facebook tried to send mail to this address. They know that the address is not valid because the mail has bounced.

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Perhaps they tried to send an email (such as EULA updates) to the specified host, and it answered in the negative - hence, "invalid"

SMTP is nonsense about how it processes - or does not process - messages "cannot deliver" evenly, but various detections can work "reasonably well" (VRFY, checking automatic replies, etc.). )

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I am sure that FB has sent you any kind of email, and from then on your mail will be deleted or deactivated ..... there for your message an error message will be returned to them, for example:

 No such user mailbox unavailable etc ..

so they can find out and deactivate their account

if you are interested to know that the error message just sends an email and wait for it to return

simple but comfortable :)

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What some companies (and possibly FB, although I don’t know for sure) do, periodically sends an email to the account, just to find out if it is "live" - ​​they will ask the recipient to click the link to it to confirm that email address is still in use.

After several such emails that did not receive a reply (or were bounced ), they will consider the email address "dead."

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