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Deliverability

Soft Bounce

A temporary email delivery failure that may succeed on a future attempt.

Definition

A soft bounce is a temporary email delivery failure that occurs when an email cannot be delivered at that moment but may succeed later. Common causes include a full mailbox, a temporarily unavailable server, or a message that exceeds size limits. Unlike hard bounces, soft bounces may resolve on their own.

Why It Matters

Soft bounces are less damaging than hard bounces but still require attention. Consistent soft bounces to the same address may indicate an abandoned mailbox or a permanent problem disguised as temporary. Too many soft bounces can still affect deliverability.

How It Works

When a temporary delivery problem occurs, the receiving server responds with a temporary failure code (4xx series). Your email service provider typically retries delivery over several hours or days. If the email eventually delivers, it is no longer counted as a bounce.

Best Practices

  • 1Allow your ESP to retry soft bounces automatically (usually 24-72 hours)
  • 2Convert to hard bounce status after 3-5 consecutive soft bounces
  • 3Monitor for patterns like many soft bounces to one domain
  • 4Check if soft bounces spike after server or DNS issues

Frequently Asked Questions

Most ESPs convert soft bounces to hard bounces after 3-5 consecutive failures over several weeks. If an address soft bounces on every send over a month, treat it as a hard bounce and remove it.

Common causes include: mailbox is full, server is temporarily down or overloaded, email is too large, auto-responders indicating vacation, or rate limiting by the receiving server.