Outlook Error : "Too many simultaneous connections"

Case: Email client gives error when an IMAP account is configured on multiple devices for gmail user mailbox. 

Reason: You can only use 15 IMAP connections per account. If you have many email clients getting messages from Gmail at the same time, you may see the "Too many simultaneous connections" error.

Solutions: Suggested fixes given below for resolving this issue - 

1. From Gsuite Admin - 

Reset a user's sign-in cookies

1. Sign in to your Google Admin console. ... 

2. From the Admin console dashboard, go to Users.

3. Click the user's name to open the user's account page.

4. Click Account to open the settings.

5. Scroll to Cookies and click Reset sign-in cookies.

6. Click Reset sign-in cookies again to confirm.

2. From User Gmail -

Please login to user webmail via mail.google.com / gmail.com and then click on the right hand bottom corner -- Last account activity -

Click on "Details" .  Now you will see all the IP's that make up the connection.  Click on the button Sign Out all other sessions and you've freed up connections. 

3. From email client -

If you use multiple email clients or devices for the same Gmail account, try closing or signing out of some or restart the email client application like Outlook / Thunderbird

In Thunderbird Settings it allows you to specify the number of Cached IMAP connections to use on a mailbox, the default being 5.

You can change this to 1 to force all users to stick to a single connection to the shared mailbox.

This can be quickly achieved by changing the ”Right Click Account -> Account Settings -> Server Settings -> Advanced -> IMAP -> Maximum number of server connections to cache” setting.

Refer the attached help guide for more details -