This is where you can see which email addresses have bounced. There are many types of bounces such as hard-bounces, soft-bounces, email blocked and much more.
A bounce occurs when a newsletter is not delivered to a recipient. A “soft” bounce is a temporary error that does not result in the removal of the recipient from the mailing list but may delay delivery to that person. A “hard” bounce is an undeliverable message resulting from an email address or domain that is determined to be unreachable after a single attempt.
Soft bounce (bounce_sb)
A soft bounce is an e-mail message that gets as far as the recipient’s mail server but is bounced back as undelivered before it gets to the intended recipient. This might happen because the recipient’s inbox is full and it may be deliverable at a later time. After three delivery attempts, it will become a hard bounce.
Transient bounce (bounce_tr)
A transient bounce is often generated by the sender’s email server which indicates that a message could not be delivered but the server is still trying. Usually, a transient bounce can be safely ignored. You might receive the following message: Warning: message still undelivered after 4 hours. Will keep trying until message is 2 days old.
Address Change (bounce_ac)
An Address Change response means a recipient has changed their address and is sending an automatic reply to notify senders of their new address.
Auto-Replies (generally in the form of an out of office notice) are usually sent by a recipient’s email client. Unlike bounces, these indicate that an email recipient is temporarily unavailable. These notifications are useful when sending time-sensitive information to recipients, as they serve to alert you that the recipient may not see it until later. These can otherwise be safely ignored.
A Challenge/Response reply is a message sent by special filtering software installed by the recipient designed to accept messages from only senders they know. This type of filter automatically sends a reply with a challenge (a question or required action) to the sender of the e-mail. If the challenge is not completed correctly, the message is not delivered.
DNS failure (bounce_df)
The email server is temporarily unable to deliver your message to an email address because of a DNS problem.
Hard Bounce (bounce_hb)
A hard bounce is an e-mail message that has been returned to the sender because the recipient’s address is invalid. A hard bounce might occur because the domain name doesn’t exist or because the recipient is unknown.
Email blocked (bounce_mb)
Indicates that the recipient’s email server is blocking email from your email server. You may see the following messages returned to you:
– 550 Message REFUSED by peer
– 552 Blocked by filters
Mailbox is full (bounce_fm)
The email server is temporarily unable to deliver your message to the recipient email address because the recipient’s email box is full.