What are Soft and Hard Bounces?

When a recipient's mail server refuses to accept one of your emails, the rejection is called a bounce. There are two flavours - one is temporary and recoverable, the other isn't.

Soft bounce

A soft bounce is a temporary delivery failure - usually something that will sort itself out by the next send. Mailblast keeps soft-bounced addresses on your list, but if the same one fails 3 times within a 4-week window it gets escalated to a hard bounce.

Common causes:

  • The mailbox is full
  • The recipient's mail server is temporarily offline or rate-limiting

Hard bounce

A hard bounce is a permanent failure. Mailblast immediately stops sending to a hard-bounced address on that list - continuing to send would hurt your sender reputation.

Common causes:

  • The email address doesn't exist
  • The recipient's mail server has blocked your domain

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