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Mail bounced, how do I tell if it's temporary or permanent?

Soft bounces (4xx) are temporary: full mailbox, slow server. Hard bounces (5xx) are permanent: address gone or blocked.

Try this first

  1. 1Read the NDR, find the three-digit code
  2. 24xx: retry after a few hours, your mail server usually does this automatically
  3. 35xx: remove from list or have the recipient check
  4. 4Repeated soft bounces after a week: treat as hard

When to bring us in

If every recipient on one domain soft-bounces, look at greylisting or MX issues on their side.

See also

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