4.1.1 Email Bounce Error
Reason
User Name In Email Address Not Valid: Delayed Message
Mailbox of the recipient’s email address is invalid or doesn’t exist and due to this message not yet delivered.
How to fix?
Check the username part (that means before ‘@’ of an email address) of the recipient’s email address for misspellings or missing letters. If an error is found, correct it in contacts list or address book for next time.
If the address looks correct, there might be an issue with the recipient’s domain. If necessary, contact the recipient another method to confirm their email address. Or contacting your mailbox provider can help sometimes.
4.1.1 – Official definition from ITEF
For the code that starts from 4.X.X
A persistent transient failure is one in which the message as sent is valid, but persistence of some temporary condition has caused abandonment or delay of attempts to send the message. If this code accompanies a delivery failure report, sending in the future may be successful.
For the code that starts from X.1.1
The mailbox specified in the address does not exist. For Internet mail names, this means the address portion to the left of the "@" sign is invalid. This code is only useful for permanent failures.
5.1.1 Email Bounce Error
Reason
User Name Of Email Address Not Valid: Message Not Delivered
The message could not be delivered because the mailbox for the recipient’s email address is invalid or does not exist.
How to fix?
Check the username part (that means before ‘@’ of an email address) of the recipient’s email address for misspellings or missing letters. If an error is found, correct it in contacts list or address book for next time.
If the address looks correct, there might be an issue with the recipient’s domain. If necessary, contact the recipient another method to confirm their email address. Or contacting your mailbox provider can help sometimes.
5.1.1- Official definition from ITEF
For the code that starts from 5.X.X
A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.
For the code that starts from X.1.1
The mailbox specified in the address does not exist. For Internet mail names, this means the address portion to the left of the "@" sign is invalid. This code is only useful for permanent failures.