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Microsoft confirms Outlook on Mac fails Exchange Server connections, no word on Windows yet

Microsoft Exchange logo blue and Microsoft Outlook logo blue on dark grey background

Over the last few days, several users are reporting on various issues about Microsoft 365 services. If you recall, there was a massive outage earlier this month due to a large-scale DDoS attack.

This week, there were performance issues once again, though, it was seemingly only limited to Germany and some other parts of Western Europe. A similar problem re-surfaced but yesterday Microsoft assured users that the issues have been laid to rest.

While the recent issue was only affecting European users, more and more people are starting to report that they too are facing different problems despite living elsewhere. There are a few threads on Reddit about the ongoing issues with multiple Office 365 apps like Outlook, Excel, or Word. Others say Teams is also having problems.

A Reddit user meatwad75892 who appears to be a system administrator summarizes the issues they have been facing:

Southeast US here; Since yesterday, have been getting a spike in reports of:

  • Outlook not opening
  • Outlook freezing after 5 minutes
  • Outlook losing connectivity with a red exclamation mark on the taskbar
  • Random oddities with Teams like clicks to navigate through the app not working

Another user Anonycron explains:

Have a few users who are unable to sign in and authenticate with desktop apps. Some connection to Microsoft appears completely down for them... even the defender scan when installing new software reports it is not able to connect. The weather widget is down. OneDrive, Teams, Word... all down. But they can use browser versions. And switching to different computers - on the same network - will occasionally work, as long as they have cached 365 logins on those computers.

The issues sound very similar to another bug that Microsoft addressed temporarily with a workaround. In that case, too, users were experiencing slow Outlook startup due to an OST sync issue.

Although most user complaints seem to be about Windows, there are a few users who are facing similar problems on Outlook for Mac.

Microsoft has acknowledged the problem as it has re-published a guidance document. While this may not apply to everyone, at least a subset of users and admins who have Secure Sockets Layer (SSL) disabled on their servers may be having issues on Outlook for Mac.

Microsoft explains:


You can't connect to a server that is running Microsoft Exchange Server from either a Microsoft Outlook 2019 for Mac or Outlook for Mac for Office 365 client after disabling Secure Sockets Layer (SSL) on the server.


The connection failure occurs because Outlook for Mac uses SSL to establish communication with an Exchange server. When SSL is disabled and secure renegotiation is implemented as defined in RFC 5746, Outlook requires the server to be in Compatible mode so that the session can be renegotiated from SSL to Transport Layer Security (TLS)

The company has provided a workaround for the issue and has recommended users enable the Compatible mode which will allow SSL to function again, and it should work even when SSL 2.0 or SSL 3.0 are blocked.

Along with that, Microsoft has cautioned users to not use the Strict mode for Threat Management Gateway (TMG) as it would prevent Outlook from connecting to Exchange Servers:


Configure the Exchange server to support Compatible mode by using the instructions from KB article 980436. This mode allows the Outlook for Mac client to establish a connection by using the SSL protocol and then renegotiate by using TLS. By using this method, Outlook for Mac can connect to the server even when SSL 2.0 and 3.0 are blocked. If you're using a security product such as Microsoft Forefront Threat Management Gateway (TMG) for managing connections to Exchange Server from outside your company, you will need to configure your TMG server using KB article 980436. External connections to Exchange Server may be blocked if the TMG server is in Strict mode.

Note: Do not configure the TMG server to use Strict mode, as this prevents the Outlook for Mac client from connecting to Exchange Server.

You may find more details in the support article (KB980436) on Microsoft's website.

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