Please login to Mimecast at https://cohp.login-us.mimecast.com/u/login/?gta=apps#/login (there should also be a shortcut on your desktop).

Next, launch the Personal Portal:

Once in the Personal Portal, you can view and manage your Inbox items, or click the 3 dots on the left navigation menu and check each of the sections highlighted below for any content you wish to manage or search. 

You will see items that you can Permit or Remove:

You will also see options to Report, Release, or Reject messages:

For more information on the Mimecast digest, please refer to this article. The digest is the email notification that you get regarding held items.

As a reminder, the following options are available when managing messages:

Release: This will release the current email On Hold to your Inbox, but future emails from this sender will still be placed On Hold
Block: Rejects the email, and adds the sender's address to your personal Block list to block future emails from this sender
Permit: Delivers the email to your Inbox, and adds the sender's address to your personal Permit list, so future emails are not put On Hold (for SPAM management policies only)