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What does “invalid recipient address” mean?

Invalid recipient address covers several validation failures:

Possible meanings:

User does not exist: No mailbox at this address. Format invalid: Address syntax is wrong. Validation failed: Server-side checks rejected the address. Policy restriction: This address type not allowed.

  • Format issues to check:
  • Missing @ symbol. Invalid characters. Domain portion issues. Local part too long.
  • Typical codes:
  • 550 with "invalid recipient." 553 with "mailbox name invalid." 5.1.1 (bad destination mailbox).
  • Response:
  • Verify address spelling and format. Suppress if confirmed invalid. Check for typos in collection process.
  • Invalid recipient is a malformed destination label. The address cannot be processed as written.
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