Because University of Minnesota email accounts require a specific type of authentication called Shibboleth, UMN Gmail accounts cannot be added as the primary email using the normal method for adding multiple Gmail accounts (Google Instructions - These will work for adding a Personal Gmail account to your UMN Account). It can be added as an email that is not default.
Instead, UMN Gmail users may obtain access to other UMN Gmail inboxes by adding Delegate access to them. This article describes adding another UMN Gmail account to your own as a Delegate to easily switch between inboxes.
Note: Delegation does not carry over to Google's Inbox application.
Enable Delegate Access from Secondary Acount
Using a web browser, sign in to the UMN Gmail for the account you want to add
Click on the Gear icon in the upper right corner of the page
In the Grant access to your account section, select Add another account
A pop-up window will appear. Enter your UMN email address (or the account you want to have access to this one)
Select Send email to grant access
Accept access to the secondary account
In your UMN Gmail, open the email from University of Minnesota Team
Select the link to Accept the Request in the email
Note that it may take up to 30 minutes for verification to complete and for the account to appear
How to use this feature
In Gmail, select your image or email address in the upper right corner
This may look like a blue circle, a custom image you added, or your full email address instead of an image
A pop-up box will appear. Select the (Delegated) email address
A new tab will open in your browser, running a second copy of Gmail. This copy will contain all the emails from the Gmail account from which you have "Delegate" access
Note: To edit delegate access, you must log in as the account you delegated to. You cannot access these settings from the delegated view.