Outage in Retarus
Multiple Services :: Delayed Delivery to Microsoft 365
Resolved Minor
September 04, 2026 - Started 12 days ago
- Lasted about 4 hours
Incident Report
Across all data centres., we are currently experiencing delays in email delivery to relays *mail.protection.outlook.com used by Microsoft 365, Exchange Online etc.
Affected are currently all services sending e-mails to said domains.
We will keep you updated.
Affected are currently all services sending e-mails to said domains.
We will keep you updated.
Components affected
Retarus Transactional Email Retarus E-Mail Security Inbound Retarus E-Mail Security Outbound Retarus Fax Services Inbound Retarus Fax Services Outbound Retarus SMS Services Retarus WebExpressTrusted by 1,000+ teams
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Latest Updates ( sorted recent to last )
12 days ago - at 09/04/2026 09:06AM
Across all data centres., we are currently experiencing delays in email delivery to relays *mail.protection.outlook.com used by Microsoft 365, Exchange Online etc.
Affected are currently all services sending e-mails to said domains.
We will keep you updated.
12 days ago - at 09/04/2026 09:09AM
Across all data centres we see Microsoft servers temporarily rejecting a large amount of emails with "451 4.7.500 Server busy. Please try again later from".
12 days ago - at 09/04/2026 10:46AM
We are monitoring the queuing systems and ensure enough storage to keep queuing messages. Sender might receive Delivery Status Notifications (DSN) in a few cases.
In the meantime Microsoft has confirmed the issue:
EX1467029 - Users may experience delays receiving email messages from external domains in Exchange Online
https://admin.microsoft.com/Adminportal/Home#/servicehealth/history/:/alerts/EX1464935
• Users may experience a delay in receiving email messages from external domains in Exchange Online.
• Users may experience intermittent “Server busy” errors, affecting multiple mailboxes.
We will keep you updated.
Latest Retarus outages
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Retarus Service Disruption - 20 days ago
Degraded Performance :: Inbound Reporting - about 2 months ago
Intermittent issues Email Security :: Degraded performance - 2 months ago
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