Either the recipient doesn’t exist, or you’ve misspelled the address. MAILBOX NOT FOUND,Invalid mailbox,USER UNKNOWN: This error is quite common and should be obvious. Some of the more common error messages follow. Some are easy to understand, and others more difficult. the original recipient account forwards a message to an account that either directly or indirectly forwards the message right back to the original recipient account.īounce messages can vary in terminology. If the recipient has a backup mail server, the email may sit in a queue until the problem is corrected.Ī less common type of error results from infinite forwarding, i.e. Typically, a bounced e-mail returns to the sender with an explanation of why the message bounced. Occasionally, a network failure or busy mail server at the sender or recipient end will cause an e-mail to bounce back to the sender. When an e-mail is returned to the sender after it has already been accepted by the recipient's email server, it is called a “soft bounce”. If the message exceeds the maximum message size specified on the email server, then the message will bounce if it exceeds that size. If the recipient exists but does not have enough disk space to accept the message (i.e., if his e-mail application is filled to storage capacity) then the message will bounce back to the sender. If the recipient's stated email address does not exist on the mail server, then the message will be rejected because there is no one to deliver it to, unless the mail server has a “catchall” address specified. The mail service has to determine if the recipient (for example, actually exists and if that account is allowed and willing to accept e-mails from the sender. If an e-mail has been accepted by a recipient's mail service, the message can still bounce. Think of it like this: the recipient’s email account didn’t even get a chance to accept or reject the email – it was bounced from the server as though it hit a hard wall. If an e-mail is returned to the sender before being accepted by the recipient's mail service, the resulting bounce is often called a “hard bounce”. The message will also bounce back to the sender if the mail server on the recipient's end is busy and cannot handle the request within a reasonable amount of time (usually 24-72 hours). it has blocked or blacklisted the address), the server will reject the message and it will consequently bounce back to the sender. If the recipient's mail server isn’t accepting e-mails from the sender's address (e.g. Once the e-mail is received by the recipient's mail server, the mail server looks at the message to determine if it will let the message pass through the server to the recipient’s email account. When someone sends an e-mail, they are telling their e-mail service to look for the mail server for the domain of the recipient (e.g. This is different from email that disappears, since the sender at least receives some indication that the message failed. First, let’s define what we mean when we say an email has “bounced”: an email that was sent was never received in the recipient’s inbox, and an error message was returned to the sender by the mail service (or mail server) at the recipient’s location.