Handling email delivery during an Opensense outage (Microsoft 365)
Overview
Section titled “Overview”During an Opensense outage, Microsoft 365 queues outbound email and retries delivery automatically. Opensense never handles the final delivery, so Microsoft’s retry logic prevents message loss. If you need email to keep flowing without Opensense while the service recovers, temporarily turn off the Outlook Add-in’s signature settings and the Opensense Stamping mail flow rule.
This article covers Opensense’s redundancy, how to monitor service status, what happens to email during an outage, and how to turn Opensense off and back on in Microsoft 365.
Service reliability and redundancy
Section titled “Service reliability and redundancy”Opensense has a 99.9% uptime record over more than 12 years. Its infrastructure is built for high availability and redundancy, so mail keeps flowing during temporary disruptions.
Opensense runs on more than 23 globally distributed servers. If one server goes offline, the others take over its traffic automatically. To avoid mail flow interruptions, make sure the Opensense IP addresses are allowed through your firewall. See Opensense IP addresses for whitelisting.
Monitoring service status
Section titled “Monitoring service status”Subscribe to the Opensense status page for updates during any disruption. It shows:
- Real-time system health
- Outage notifications by service region
- A history of past incidents
What happens to email during an outage
Section titled “What happens to email during an outage”- Queue and retry
- Microsoft 365 mail servers queue the email and retry delivery automatically until Opensense is reachable again.
- Non-delivery report
- If retries fail after the maximum retry period, the sender gets a non-delivery report (NDR), or bounce, with the reason for the failure and suggested fixes.
Turning off Opensense during an outage
Section titled “Turning off Opensense during an outage”
Turning off the Outlook Add-in signatures
Section titled “Turning off the Outlook Add-in signatures”This stops the Outlook Add-in from inserting or previewing signatures in email.
- Sign in to the Opensense portal.
- Go to Manage > Domain Settings > Outlook Add-in (New UI).
- For each domain, turn off Automatic Signatures and Plain Text Preview.
The settings apply per domain. Changes take effect immediately, and stop all client-side previews and insertion.
Turning off server-side Stamping
Section titled “Turning off server-side Stamping”When the Outlook Add-in is inactive, Opensense can still apply the plain text block through mail flow rules in Microsoft 365. To turn off this fallback:
- As a Microsoft 365 admin, sign in to the Exchange admin center.
- Go to Mail flow > Rules.
- Find the rule named Opensense Stamping, and disable it.
Disabling the rule stops all server-side stamping, so no signatures are applied while Opensense is down.
After the outage
Section titled “After the outage”When the outage is resolved, turn the Outlook Add-in settings back on for each domain, and re-enable the Opensense Stamping rule.
What’s next
Section titled “What’s next”- Microsoft 365 integration overview (change request): the connectors and mail flow rules, including Opensense Stamping.
- Configuring the Outlook Add-in in Domain Settings: what each add-in setting does.
- Opensense IP addresses for whitelisting: the addresses to allow through your firewall.