What is a bounce?

• When an email message cannot be delivered to an address, a response is sent back from the receiving server. Based on an evaluation of the response, the bounce is considered either a hard or soft bounce.

What is a hard bounce?

• When the response from the receiving server indicates that the address is invalid (examples: "user unknown", "no such user here", "invalid recipient", etc...), the bounce is classified as a hard bounce.

What is a soft bounce?

• When the response from the receiving server indicates that the address is valid (examples: "mail box full", "temporary fail", "spam block") the bounce is classified as a soft bounce.

When is a contact's email address marked as invalid by Cordial?

• After the first hard bounce.
• After six or more consecutive soft bounces have occurred across a timeframe of at least 21 days.

Multiple soft bounces received within a 24-hour period only increases the total count by one.

If less than 21 days (three weeks) have passed during a string of consecutive soft bounces, the contact is not marked as invalid. Once the pattern has occurred for more than three weeks (at least six times in a row without a successful send), the address will be deemed undeliverable and marked as "invalid".

How are email addresses marked as "invalid" handled?

• Any address marked as invalid are automatically suppressed from any message send.
• Addresses marked as invalid are NOT included in the audience count total when building an audience for an email message.
• Addresses marked as invalid are included in the audience count total when searching for contacts in the "search" outside of the message creation process.

Am I able to identify and correct issues with an email addresses that has been marked as invalid?

• While it is possible to update a subscriber from invalid to valid status using the API call PUT<path>/contacts that's described below, it is also necessary, if the contact was invalidated due to a "hard" bounce, to contact Cordial support and request that the contact be removed from any MTA suppression lists. 
• You can overwrite the invalid setting by making a PUT call for the contact record via the REST API. This should only be done when the email address was marked as invalid due to a typo (examples: "user unknown", "no such user here", "invalid recipient", etc...) and the email address is also corrected during the PUT.