Suppression list (blacklist) system

SmartRelay shares the suppression list management system that is used by Contactsend.

Unknown user/invalid recipient bounces, for example, are immediately added to a suppression list as soon as they are received and processed. For privacy reasons, each such suppression list is customer-specific.

Other bounces are managed using smart, time-based, temporary suppression logic. This adds a recipient to, or removes a recipient from, the relevant suppression list until either:

  • The seven week time limit is reached, with no successful delivery
    • The recipient is added to the suppression list permanently


  • A successfully delivery is recorded before then end of the time limit
    • The recipient is marked as valid

This logic ensures that:

  • False positives are reduced to a reasonable minimum, even for infrequently used mailboxes
  • Mail service providers (MSPs) do not see many messages sent to a potentially disabled mailbox before the attempts stop permanently
    • MSPs consider this problem a symptom of bad list management practices, which has a negative impact your sender reputation

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