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What is the difference between soft (temporary) and hard (permanent) bounces?

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    Overview

    Think of hard bounces as permanent errors and soft bounces as temporary errors.

    We will stop any further attempts at delivery after one hard bounce.

    With soft bounces, we keep trying to deliver but eventually we will stop any further attempts at delivery in accordance with the receiving ESP’s feedback.

     

    A more detailed explanation

    Failed messages are quite nuanced in both cause and effect. Webhooks primarily delineate between two types of failure persistence: temporary (soft bounce) and permanent (hard bounce); note, a message “bounces” when rejected by a receiving SMTP server.

    • Temporary failure webhooks fire for events such as a full mailbox; we try later on a few more times, but if delivery continues to be unsuccessful, we stop retrying. These failures do not add the email address to the “Bounces” table in the Suppressions tab of your Control Panel.

    • Permanent failure webhooks fire for events in which the recipient was not found, or was determined to not exist, within the recipient server’s environment. These failures - and thus the firing of the webhook - also occur due 1) soft bounced/temporarily failed emails exhausting all (re)delivery attempts, 2) ESP blocks due to poor sender domain or IP reputation, and 3) the email address is listed on one of Mailgun’s three Suppressions tables (Bounces, Complaints, and Unsubscribes) for your domain.

      • For permanent failures due to invalid recipients, we do not attempt any further deliveries after encountering the hard bounce. These failures do add the email address to the Bounces table in the Suppressions tab of your Control Panel.

      • For permanent failures due to all of the other reasons, we also do not attempt any further deliveries after encountering the hard bounce. However, these failures do not add the email address to the Bounces table in the Suppressions tab of your Control Panel.

      • If an email address is in the Bounces, Complaints, and/or Unsubscribes tables, Mailgun will not attempt delivery of future emails submitted to our system that contain said address.

      • Note: Bounces, Complaints, Unsubscribes, and Whitelists are available programmatically through the respective APIs.

     

    Need Support?

    Our Support Team here at Sinch Mailgun is happy to help! Reach out to us in the Support section of your Mailgun Control Panel, and we'll be with you shortly!