I regularly work with multiple Azure Active Directory and Office 365 tenants, recently I wanted to utilise a domain that was attached to a tenant that had expired in December 2015, but did not know how to recover it.
The various portals that you can utilise offer very little guidance.
Azure Active Directory was a little more than useless
but the new Office 365 portal offered hope, with an indication as to which tenant it was attached to.
So now what are my credentials?
Fortunately there is a link to reset your account details which were emailed to my @outlook.com email address which I added when creating the tenant.
So once I had recovered my credentials then I could access the portal and delete the domain.
If you get the message below, you have objects(users, groups or contacts) in the directory that still have the domain you are trying to delete associated to them.
The domain is now removed and can be utilised in another tenant.