A hard bounce is an email that could not be delivered because the recipient's email address is invalid or the recipient's email server won't accept emails. There are other reasons why a hard bounce happens, but the above 2 reasons are the most common ones.
A hard bounce indicates a permanent failure. We remove hard bounced email addresses from our platform in order to maintain our mail server reputation and also our user's reputation (you).
A soft bounce is an email that couldn't be delivered because of temporary reasons. When an email address soft bounces, we will continue to attempt to deliver the email for another 2 times. If the email still soft bounces after we've attempted delivery for those period, it will be logged as a soft bounce on the user's report.
If an email address continues to soft bounce across multiple email sends, the address will eventually be considered a hard bounce and cleaned from user list. We'll allow 3 soft bounces for an email address before converting a soft bounce into a hard bounce.
While there are many reasons an email address may soft bounce, below are some common reasons this could happen.
- Mailbox is full (over quota).
- Recipient email server is down or offline.
- Email message is too large.