This document describes how to create a shared mailbox in Office365, such as the one used by the SpeakEasy office. The document also describes how to add or remove users from that mailbox.
Firstly, login to the: Office 365 Admin Centre. The user must have appropriate administration rights to be able to do this.
Then, simply follow the instructions that are provided by Microsoft on the following page: How to Create A Shared Mailbox
If in doubt, it is recommended that one take a look at the configuration of one of the existing shared mailboxes and try to set up the new shared mailbox using similar settings.