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Outage in Exclaimer

Delivery delays for messages sent from Outlook and Exchange

Resolved Minor
September 22, 2026 - Started 21 days ago - Lasted 17 days
Official incident page

Incident Report

Summary AI Generated

**Exclaimer experienced delivery delays affecting a small subset (~0.02%) of messages routed through its Mail Routing for Office 365, caused by an issue on Microsoft's servers.** Impacted messages appeared as temporary deferrals rather than delivery failures, with no confirmed message loss, and successfully delivered messages still had signatures applied as expected. Mail delivery normalized on September 27 following changes on Microsoft's servers, with Exclaimer continuing to work with Microsoft to establish a root cause.

Exclaimer engineers are investigating a delivery delay affecting some messages sent from Outlook and Exchange to Exclaimer Cloud. Some of these messages may be retried by the sender and may appear as temporary deferrals rather than delivery failures. We are not currently aware of any confirmed message loss and will provide updates as we learn more.

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Latest Updates ( sorted recent to last )
RESOLVED 4 days ago - at 10/09/2026 08:40AM

The original impact of the issue has been mitigated by Microsoft changes. Exclaimer Engineers are continuing to work together with Microsoft to establish a root cause.

If you have any questions or concerns, please reach out to our great support team, who will be more than happy to help answer any questions.

MONITORING 16 days ago - at 09/27/2026 07:33PM

Mail delivery has resumed as normal and our engineers are seeing significantly less errors. The team are awaiting confirmation of a fix implemented on Microsoft servers and will be monitoring until tomorrow morning to confirm.

IDENTIFIED 21 days ago - at 09/22/2026 03:19PM

Exclaimer has identified that a small subset of messages (~0.02%) are delayed when routed through Exclaimer due to a suspected issue within Microsoft's servers. This has been raised with Microsoft to investigate alongside Exclaimer Engineers.
Sent messages will be received with a signature applied, as expected.

If you are seeing issues with message deliverability, please reach out to our support team, who will be happy to assist.

INVESTIGATING 21 days ago - at 09/22/2026 10:58AM

Exclaimer engineers are investigating a delivery delay affecting some messages sent from Outlook and Exchange to Exclaimer Cloud. Some of these messages may be retried by the sender and may appear as temporary deferrals rather than delivery failures. We are not currently aware of any confirmed message loss and will provide updates as we learn more.

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