Note that the email bounce message includes the email address you were attempting to send to. In the “[email protected]” bounce examples above, the mail server “example.com” doesn’t have an account for anyone with the email name “someone”.A couple of common reasons: Nine times out of 10, this is the same as “mailbox not found.” The other 10% of the time it could mean there’s a problem with the recipient’s email account. Check to make sure you have the email address correct, wait a while, and try again; if it still bounces, contact the recipient some other way.SMTP is an acronym for Simple Mail Transfer Protocol, which is the protocol used to transport email messages from computer to computer until they reach their destination.SMTP is used between email programs, which are SMTP , which forward email to its destination.Remember, though – a message you get may not be worded exactly as I list it here.
This means that the mail server you’re attempting to use – the “example.com” part, in the examples above – doesn’t exist. This is the memory that is lost when the computer is powered off, and the memory that is reloaded when the computer boots.Anyone trying to send to an old “attbi.com” email address might get this message in return.This is a terribly obscure error message that is becoming more and more common as ISPs try to crack down on spam Spam is tricky.SMTP is then also used between SMTP mail servers as they forward the message on to the next server, until the message reaches its final destination mail server.The words”MAILBOX NOT FOUND” or “User unknown” are key, and might actually be expressed in different words, depending on the reason for the failure.