Impersonate service for read only mailbox data

Hi All,

I need to setup a "Service account" to be able to read all mailboxes, really only Subject, Sender,Recipient but happy for it to be all. 

I was planning to use the impersonate  feature,new-managementroleassignment", but I am not sure what Role would allow this or if I would need to create a new role.

If anyone know which role allows this or the require configuration of a new role please let me know?

Thanks for your time in Advance. 

Craig

Craig G