Getting sensitivity label working for specific domain

Good morning all 

I am trying to setup a sensitivity label to work so anyone with '@mail.com' will have access to a document that has this label. I have attempted to apply this in the  control access settings with the label under 'Add specific email addresses or domains'

However for the life of me, I cannot get this to work, I have tried "*@mail.com. mail.com, mail.com", nothing seems to work. I have run through the MS material on this and can't see anything specific to setting this up. Has anyone been successful in setting this up? Is there a trick I am missing?

Grateful for anyone who can help on this!