Hi all,
Here is some more specific information regarding email bounces:
Soft bounce: A soft bounce occurs when an email makes it to the recipient's mail server, but it doesn't get delivered. A soft bounce might occur because the recipient's mailbox is full, the server is down or swamped with messages, or the message is too large.
Multiple bounce: Sometimes the reason for a soft bounce is unclear, so contacts aren't opted out unless there are repeated bounces. After five consecutive bounces, the message becomes considered a "multiple bounce" and the contact is opted out.
Hard bounce: A hard bounce occurs when an email message is returned to the sender and is permanently undeliverable. It can happen if you send an email to an invalid address or if the email recipient's mail server has blocked your server. In cases where the server initially accepts a message, the email status could be shown as "Sent" then switched to "Undeliverable" when the bounce occurs. After one hard bounce, the contact is opted out.
Best,
Julia