After the appropriate rights have been delegated to your user, please follow these steps to open another Office 365 mailbox:

In a web browser

1. Log into Office 365 at https://365.ucdavis.edu
2. Click on your profile icon at the top right corner of your web browser
   
   Note: if you do not have a profile photo, your initials will be displayed
3. Click the link "Open another mailbox"
   
   Note: screen might look different
4. Type in the account of the other Office 365 mailbox and click "Open"
   
5. The other mailbox should open in a new tab or window

Using Outlook 2019 or 2021

1. Go to File > Info
   
2. Click on Account Settings and on Account Settings... again
   
3. In the Email tab, select your email address and click Change...
   
4. Click the More Settings... button
   
5. Go to the Advanced tab and click the Add... button
   
6. Type in the mailbox address you want to add
   
7. Click OK to close the Add Mailbox window
8. Click OK to close the More Settings window
9. Click Next to close the Change Account window
10. Click Close to close the Account Settings window
11. The other mailbox should appear in Outlook's left pane under your primary account mailbox