Don’t Forget To Do This Before Migrating to MediaTemple’s Single Login
After years of bouncing between a dozen or two MediaTemple hosting accounts, they've finally rolled out a single login to manage and access them from. Before you hit the switch and click the button to link all your accounts, make sure all the accounts you want linked have your primary email in them as an owner or admin.
If not, there's no way (currently) to link another MT account after you've set up the single login account. Might be a few weeks before they add that functionality, or you may need to request it via the account center.