When an email is rejected by a subscriber's email server, it's called a bounce.
This article covers:
Hard bounces
A hard bounce indicates a permanent reason an email cannot be delivered.
An address that hard bounces is added automatically to your bounce list. Later email campaigns skip it with the status Previous bounce.
If the address is correct, you can remove it from the bounce list: click Unbounce on the recipient's row in the campaign's Recipients tab, or edit the contact and click Unbounce address under the email field. Each month you can unbounce up to 2% of your total number of contacts (1 if you have fewer than 50 contacts).
Reasons for a hard bounce include:
- Recipient email address doesn't exist
- Domain name doesn't exist
- Recipient's email server has blocked delivery
Soft bounces
Soft bounces usually mean there's a temporary delivery issue.
When an email address soft bounces, it will immediately display as a soft bounce in the email campaign report.
Later email campaigns are still sent to an address that has soft bounced. If the contact opens or clicks one of your emails, the soft bounce is removed from the contact.
There are many reasons for a soft bounce, including:
- Mailbox is full (over quota)
- The recipient's email server is down or offline
- The email message is too large
When tracking your email campaign responses, you'll see hard bounces marked in red, and soft bounces marked in yellow:
What causes high bounce rates
High bounce rates are often caused by lists that have gone stale, or by addresses that were improperly entered or imported.
Internet service providers (ISPs) have limits for bounces, unsubscribes, and abuse complaints. Naturally, we're required to enforce these limits.
If bounce rates are too high, it could prompt a warning or suspension on your account.
Bounce rate limits vary between ISPs and email providers, and they change throughout the year based on incoming email volume.
Because these limits are variable, and to avoid giving too much information to spammers, ISPs do not publicly release their limits or their spam filter criteria.