User Impact:
Users may be unable to connect to the Exchange Online service.

Current status:
Microsoft have confirmed that impact has been remediated and are continuing to monitor service health to ensure connectivity remains unaffected. They have applied a long-term fix and we’re waiting for confirmation that this fix will prevent this issue from happening again.

Scope of impact:
Impact is specific to a subset of users who are served through the affected infrastructure.
Root cause:
A subset of network infrastructure became degraded, causing impact to service availability.

Workaround:
If Outlook has become unusable, please use Outlook Web Access, which is available at https://email.essex.ac.uk and appears to continue to function without issue.

In the native Mail app (Mail.app) on your iPhone or iPad, you can’t send or reply from your Outlook.com, Office 365, or Exchange Server 2016 email account after you upgrade to iOS 11. Note These issues don’t occur in iOS 10.

This issue occurs because the Mail app on iOS 11 is not compatible with Outlook.com, Office 365, or Exchange Server 2016 running on Windows Server 2016.

To work around this issue, download the free Outlook for iOS client from the App Store. The Outlook for iOS client fully supports various email services, including Outlook.com, Office 365, and Exchange Server 2016.

For more information see: https://support.microsoft.com/en-gb/help/4043473/you-can-t-send-or-reply-from-outlook-com-office-365-or-exchange-2016-i