1. Sign-in to your Gmail account within Outlook for Mac. This is for users who are on Build 0902 and higher. Have you already added your Gmail account to Outlook then see, Improved auth for existing Gmail users.
2. Download and install the GSSMO tool by Google to use Microsoft® Outlook® effectively with G Suite.

1. Gmail Contacts Outlook For Mac
2. Microsoft Outlook Email For Mac
3. Outlook Mail On Mac

BEFORE YOU BEGIN
Read the system requirements and the install steps before using GSSMO to sync your data with G Suite. Learn More.
For details on the latest features, enhancements, and fixes for GSSMO, see What's new in GSSMO.
DOWNLOAD .EXE FILE (RECOMMENDED FOR USERS)
This .exe file is for installation on Windows^® machines only but you can download it using any operating system. Download GSSMO
DOWNLOAD .MSI FILE (RECOMMENDED FOR ADMINS)
This .msi file is for installation on Windows machines only but you can download it using any operating system. Download 32-bit edition | Download 64-bit edition

Symptoms

In Microsoft Outlook 2016 for Mac, you are repeatedly prompted for authentication while you're connected to your Office 365 account.

Cause

This issue occurs because of the presence of duplicate tokens in the keychain.

Resolution

Outlook for Mac and Gmail always worked fine until the Catalina update. Now Outlook won't sync any folders, receive or send mail. All sent mail goes to 'draft' folder and won't send. I have uninstalled and reinstalled, with no correction. When setting up Outlook, you are taken to the Google page that asks to verify your account.

To resolve this issue in Outlook 2016 for Mac, install the February 2017 Outlook update (version 15.31.0) from the following Office website:

Workaround

To work around this issue, delete any cached passwords for your account, and also delete any modern authentication tokens from the keychain. To do this, follow these steps.

Gmail Contacts Outlook For Mac

Note

Microsoft Outlook Email For Mac

These steps affect all Office applications that use modern authentication.

Outlook Mail On Mac

1. Quit Outlook and all other Office applications.

2. Start Keychain Access by using one of the following methods:

   • Select the Finder application, click Utilities on the Go menu, and then double-click Keychain Access.
   • In Spotlight Search, type Keychain Access, and then double-click Keychain Access in the search results.

3. In the search field in Keychain Access, enter Exchange.

4. In the search results, select each item to view the Account that's listed at the top, and then press Delete. Repeat this step to delete all items for your Exchange account.

5. In the search field, enter adal.

6. Select all items whose type is MicrosoftOffice15_2_Data:ADAL:<GUID>, and then press Delete.

7. In the search field, enter office.

8. Select the items that are named Microsoft Office Identities Cache 2 and Microsoft Office Identities Settings 2, and then press Delete.

9. Quit Keychain Access.

   Note

   When you start Outlook, you are prompted to authenticate.