Fixes or workarounds for recent issues in Outlook for Mac

Last updated: January 2017

Outlook for Mac crashes and slow performance

Last updated: December 1, 2016


After updating to 15.28, some Outlook 2016 for Mac customers are experiencing high CPU usage.


A fix will be coming out in the next release, but as a workaround customers can turn off Automatic Language Detection by doing the following:

  1. Open a new, blank email.

  2. Click in the body of the email, and then on the Edit menu, select Language >Language.

  3. Clear the Detect language automatically check box and select Default.

Last updated: January 2017


Apple released macOS 10.12 Sierra on 9/20/2016. Some customers are reporting Office 2016 for Mac applications are closing unexpectedly, or crashing when an Office application is launched, or when the computer is moved between Wi-Fi networks (e.g. moving a laptop from home to work).

Customers in a workplace or school network configuration who wish to upgrade to macOS Sierra should update to macOS Sierra 10.12.2 or later, for improved stability specific to proxy networks.


Turning off “Auto Proxy Discovery” or “Automatic Proxy Configuration” is a possible workaround, if allowed by your organization’s network configuration.

  1. Go to System Preferences and open Network.

  2. Click on Advanced and go to Proxies.

  3. Check if "Auto Proxy Discovery" or "Automatic Proxy Configuration" is turned on.

Contact your local network administrator for more information on your network settings.

We will update this content when more information is known, including a fix or additional workaround.

Outlook for Mac issues affecting email message, attachments, and other features

Last updated: January 27, 2017


If you are running build 15.30, you may be repeatedly prompted for authentication when you're connected to your Office 365 account.


This is a known issue that has been fixed in Insider Fast build 15.30.170117. As a temporary workaround, see Outlook 2016 for Mac repeatedly prompts for authentication.

Last updated: January 25, 2017


When creating a new calendar event or appointment in Outlook 2016 for Mac version 15.30, you are unable to categorize it and the Categorize icon appears grayed out.

Outlook 2016 for Mac version 15.30 categorize calendar appointment icon grayed out


We are working on a fix estimated for the next release. As a temporary workaround, you can save the calendar item without categorizing it and then reopen it again. The Categorize icon should be enabled.

When replying to an email message or creating a new one containing an email signature, you receive the following error message:

"Some of the files in this web page are not in the expected location. Do you want to download them anyway? If your sure the Web page is a trusted source, click Yes."

Our engineering team is currently working on a fix for this issue. We'll post back with more information when a fix is released out to our customers.

In Outlook for Mac 15.22 you may notice that the Emacs-style keybindings no longer work properly. We apologize for any inconvenience this issue has caused and want to assure you that the Outlook team is working on a fix. We will update this article when the issue is resolved.

When composing emails, automatic language detection is not working in the new editor for Outlook 2016 for Mac (versions 15.20 and later).

We’ve recently released the fix for this feature in our latest update version 15.28.0 (Build 16111501) released on 11/15.

  • Use Help > Check for Updates from any of the Office 2016 apps to get the latest build.

  • If for some reason you can’t update via Help, you can manually download and install the new build from this article.

Please note that enabling this feature in version 15.28 has a different workflow from the previous mail editor (versions 15.19 or earlier). To enable automatic language detection, please refer to this article: Let Outlook 2016 for Mac automatically detect and spell check languages in your emails.

When pasting text and images in the new mail editor for Outlook 2016 for Mac (version 15.20 or later), paste doesn't default to 'Match Destination Formatting.'

We’ve recently released the fix for this feature in our update version 15.27 (Build 16111501).

  • Use Help > Check for Updates from any of the Office 2016 apps to get the latest build.

  • If for some reason you can’t update via Help, you can manually download and install the new build from this article.

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