Here's how to get the details of any connections to an Exchange mailbox:
Get-MobileDeviceStatistics -mailbox foo.user |select deviceuseragent,lastsuccesssync,deviceid
Data Wipe an iPhone that has an Exchange account on it:
Clear-MobileDevice foo.user
Get-MobileDevice -mailbox foo.user |Clear-MobileDevice
If you need to cancel the wipe:
Get-MobileDevice -mailbox foo.user |Clear-MobileDevice -cancel
If you need to simply remove the relationship:
Get-MobileDevice -mailbox foo.user |Remove-MobileDevice
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NOTES:
get-help mobile
get-help get-mobiledevice
get-help Get-MobileDeviceStatistics -full
get-help clear-mobiledevice -full
get-help remove-mobiledevice -full