Office staff unable to access remotely our company email via Outlook

Our business uses Outlook for all email correspondences from potential clients via our website and general correspondences. It is a critical part of our business. The problem is:

When my office staff began working remotely, I provided them with the password so that they could monitor all of the emails coming in. The problem is they do not see any of the emails coming through. They can email out, but that is it! They do not see any of the incoming emails. 

Does anyone know how I can fix this? This is a very important part of their job.

Chrisanne