You attempt to activate an iPhone or Android device with Exchange ActiveSync but receive the following error message:
You have 10 phone partnerships out of the maximum allowed 10 partnerships. After you reach the maximum, you can't create additional partnerships until you delete existing ones from your account. To do so, sign in to Outlook Web App, click Options > Phone > Mobile Phones, and delete any unused partnerships.
The account setup on the iPhone completes but mail does not sync while Android devices display the following message:
You have reached the maximum number of devices allowed in your device network
The reason why these messages are being displayed is because by default, Exchange 2010 actually has a limit on how many devices you can set up with ActiveSync and the default is 10 devices. This usually isn’t a problem with regular users but if you’re an administrator that regularly sets up devices for users, you may find that you will quickly exceed the limit.
The way around this is to either delete some devices via the following instructions in OWA:
Sign in to Outlook Web App, click Options > Phone > Mobile Phones, and delete any unused partnerships.
Or use the Set-ThrottlingPolicy with the EASMaxDevices switch as shown in the following TechNet article to increase the maximum amount of ActiveSync devices allowed: