Issue Summary

Our public documentation: https://support.atlassian.com/statuspage/docs/view-quarantined-subscribers/, states "Email subscribers are moved into the "Quarantined" tab when we try to deliver mail to them but encounter a permanent failure".  However it has been discovered that this is not happening, and even though our email notification to a subscriber receives a hard bounce, the error being returned from our mail provider Malgun is a "generic" error which does not match our expected results. As a result, the email subscriber is not triggering the quarantine process.

Additionally, there are scenarios where emails are being added to a Sendgrid suppression list for a particular sendgrid account instead of being quarantined, and resolving this requires intervention from Engineering. It is not known if this is related due to a logic failure or a historical implementation

Steps to Reproduce

• Send an email to an email address via Mailgun that should product a hard bounce error.
• If the response from Mailgun APIs is "generic", the quarantine process is not triggered

Expected Results

As per our documentation - Email subscribers are moved into the "Quarantined" tab when we try to deliver mail to them but encounter a permanent failure.

Actual Results

The quarantine process is not triggered even when the failure is permanent, and for subscribers sent via the Sengrid provider, they can be suppressed without the Customer (or Support) being able to identify this.

Workaround

N/A