When an email is rejected by a subscriber's email server, it's called a bounce.

Hard bounce

A hard bounce indicates a permanent reason an email cannot be delivered. In most cases, bounced email addresses are removed automatically and immediately from the active subscribers and placed in the Cleaned portion of your list. Cleaned subscribers will be excluded from future campaign sends to this list. While there are many reasons an email address may hard bounce, below are some common reasons this could happen.

• Recipient email address does not exist.
• The domain name does not exist.
• Recipient email server has completely blocked delivery.

Soft bounce

Soft bounces typically indicate a temporary delivery issue to an address and are handled differently than hard bounces by MailChimp. When an email address soft bounces, it will immediately display as a soft bounce in the email campaign report.

If an email address continues to soft bounce in additional email campaigns, the address will eventually be considered a hard bounce and cleaned from your list. We'll allow seven soft bounces for an email address with no subscriber activity and up to 15 soft bounces for subscribers with previous subscriber activity 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.
• The email message is too large.

High Bounce Rates

High bounce rates are often caused by lists that have gone stale or addresses that were improperly entered or imported.

Internet service providers (ISPs) have limits for bounces, unsubscribes, and abuse complaints, and Upsales is required to enforce these limits. If these 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.