Bing’s failover process allows customers to take advantage of the lower cost of email and SMS whilst maximising delivery success by falling back to postal mail should email or SMS delivery fail.

How does it work?

When failover is enabled on your account, each email or SMS that cannot be successfully delivered (i.e. "bounced" or returned with a Non Delivery Report - NDR) will automatically fail over to the postal address that was supplied in the document. A failover "chain" can also be created so that (e.g.) email can failover to SMS, then to postal should the SMS also fail.

When does failover occur?

Email delivery can fail for a number of reasons, two common issues are:-

  • Email address is invalid.
  • User Unknown at destination.  Typically the recipient has left the organisation and has failed to provide a new email address.

Email delivery can have three results: successful delivery, temporary failures that will be automatically retried and permanent failures such as User Unknown.

Bing’s failover mechanism is triggered by permanent failures that occur within 7 days of sending the email. NDRs (email bounces) received after 7 days are handled as returned mail and failover will not occur (The majority of email failures happen within minutes). The 7 day period is configurable if required.

SMS may fail if the supplied phone number is invalid or incorrect, or if the recipient's phone is switched off or otherwise unavailable for a predetermined time. SMS failover time is 24 hours by default, also configurable if required.


All messages that fail over are added to a failover report produced twice weekly and emailed to the configured recipient for the account. Failover reports are also available in the Bing customer portal.

The failover API is an alternative programatic method for querying letters that failed over. See link for further information and usage.

Contact Bing Customer Service to get set up for Bing failover.