Heysender incident
Microsoft has issues receiving email
Heysender experienced a minor incident on September 4, 2026 affecting Outgoing SMTP, lasting 1h 19m. The incident has been resolved; the full update timeline is below.
Affected components
Update timeline
- monitoring Sep 04, 2026, 12:00 PM UTC
Since 9:50 CEST this morning Microsoft has had issues receiving email. This means that many emails sent to Office365 recipients will result in a soft bounce with this message: 52.101.68.10 failed after I sent the message./Remote host said: 451 4.7.500 Server busy. Please try again later from \[REDACTED\]. (S77714) \[[DB1PEPF000509E3.eurprd03.prod.outlook.com](http://DB1PEPF000509E3.eurprd03.prod.outlook.com) 2026-09-04T08:16:36.825Z 08DF04AEA47F75BA\]/ If you have access to the Office365 admin page they have created an issue to follow here: We're monitoring the issue but for now there is nothing we can do to force emails through. Emails sent during Microsoft downtime will be tried again for the following 48 hours until delivery is possible. (We're mainly creating this issue to have a place to point clients to for updates. There is nothing we can do inhouse to solve the issue.)
- resolved Sep 04, 2026, 01:20 PM UTC
This incident has been resolved by Microsoft. We're working on emptying the queues and we expect all email to be delivered soon.