Make sure that you configure your email application to use the full email address as username instead and this issue should be resolved.

This is a common error which happens when the username that you are authenticating your emails with is not correct. This can be addressed by the owner of the recipient address. Your mail server might also be unable to determine the correct route to send your email message because of a DNS configuration error with the recipient domain’s MX records. You also might have exceeded the maximum number of e-mails you are allowed to send per hour, in which case you should allow some time and then resend the mail. The recipient’s email address might be misspelled. This type of error can be due to a variety of reasons. After that timeframe, you should receive a notification in case the delivery has failed. The server will usually try to resend your message over a 48 hour period. The above errors relate to temporary problems with a mail server. These error messages are showing that the recipient’s mailbox is full and the server will not accept any more messages until the user make more space available.

Check that you have the spelling of the email correct. The most common reason for all of the above errors is that the email address was typed incorrectly or the mailbox that you are trying to reach no longer exists. We prepared a list of common bounce back errors to help identify why your email might not be delivered to its intended recipient(s):

These returned emails are referred to as bounce-back emails.

Often, if an email delivery fails, the original email is returned to its sender with an error explaining what caused the issue.

Server email bounce back message gmail