When adding delegate mailboxes, the following terminology is used:

• Primary Address: This is the email address of the primary user who wants delegate access to another user's (the delegate's) mailbox, in addition to their own mailbox.
• Delegate Address: This is the email address of the user, whose mailbox the primary address user will have delegate access to.

Note:

When delegating access, perform the following on the mailbox that needs to view the delegated mailbox and add the "delegated mailbox" to this users account.

To add a delegate mailbox: (For example below, Joseph Hassranah would like to have delegate mailbox access of Daniel Vazquez)

1. Log on to the Mimecast Administration Console.
2. Click on the Directories | Internal Directories menu item.
3. Click on the Internal Domain of the primary address. 
4. Click on the Domain of the primary address. The domain's email addresses are listed (utilize the search bar to locate the specific primary address requesting delegate access).
5. Click on the Email Address of the primary address. This displays the Address Settings.
6. Click on the Add Delegate Mailboxes button from the top toolbar. Any current delegates for the primary address are listed.  
7.  Click on the Add Delegate Mailboxes button to select the delegate mailbox address. 
8.   Click the Lookup button to the right of the "Delegate Mailbox" field. (Be patient, wait about 10-15 seconds for search to process)
9.  Type the Name or Email Address of the "Delegated Mailbox" in the search field and click on the Search button.
10. Select the Email Address from the list of result, then click Save and Exit button.  

You have now completed the process.

The delegate account can be accessed by signing in to your personal Mimecast account and selecting your user profile icon in the upper right corner.  You will see your account on top and the delegate at the bottom, select the "Open" link to access the delegate account.