Can't send as a delegated user

Hi,

I am exploring Office 365 for a new setup.

I want to have users logging on to OWA with their personal credentials and having delegated access to their 'group mailbox' as well as their own personal mailbox. e.g. joe.bloggs@ and sales@

I have set up a test using the 2 licences that I currently have. I have added the mailbox 'test' to my mailbox sucessfully. However if I open an email sent to test@ and reply, it goes out from my address.

I have set my user for both 'Send as' and 'full access' on the delegation page of 'Test'.

Please can someone tell me what I need to do?

Thanks!