Zendesk sends email notifications for changes, including ticket updates, forum updates, and system messages. When one of these email notifications is returned, or bounced, from the server it is sent to, Zendesk will mark the email address as undeliverable and no longer send email to that address. If an address that is marked as undeliverable becomes deliverable, an agent can manually mark it deliverable.
This article contains the following sections:
About the email bounce process
When an email notification cannot be delivered to an address, the receiving server will often send a notification back to Zendesk indicating that the message was not received. This is known as a bounced email.
A bounce is considered a hard bounce when the notification Zendesk receives from the server indicates that it is a permanent failure. A bounce is considered a soft bounce when the notification Zendesk receives from the server indicates that it is a temporary failure.
After a hard bounce, Zendesk will mark the email address as undeliverable and no longer send email to that address. After a soft bounce, Zendesk will attempt to send the email again. After ten failed attempts with soft bounces, Zendesk will mark the address as undeliverable and no longer send email to that address.
When an email notification bounces, the email address is flagged as undeliverable in the ticket and in the user's profile. You and your agents will not be notified and there will not be a resulting suspended ticket.
Understanding how undeliverable email addresses are marked
When an email address receives a hard bounce, Zendesk marks it as undeliverable and stops sending email to that address. If the primary address is not deliverable, and the user has multiple email addresses, Zendesk will send email to any other address that is deliverable.
When a user's email address is marked as undeliverable, the adress is flagged in the user's profile and in the ticket. You and your agents will not be notified when this happens, and there will not be a suspended ticket.
There might be times when an undeliverable address becomes deliverable again, so an agent can manually set an undeliverable email address to deliverable. Any future bounce notifications, however, will return it to the undeliverable state. When you manually set an email address to deliverable, it does not resend email notifications on existing tickets. You can see which comments did not send notifications by viewing the ticket's events (see Viewing all events of a ticket).
How undeliverable emails are marked in the user profile
In the user profile, an undeliverable address is flagged.
How undeliverable emails are marked in the ticket
In the ticket, an undeliverable email address for a ticket requester is flagged. Undeliverable addresses for CCs are not flagged in the ticket, but are flagged in their user profiles. You can still update the ticket, but Zendesk will not send email notifications to any user with an undeliverable email address.