You can use Office 365 admin center or Windows PowerShell for deleting Exchange Online mailboxes. The effect of deletion on the mailbox varies according to the process used. Soft-deleted user-mailbox is that mailbox which is deleted via Office 365 admin center or using cmdlet in Exchange Management Shell. This mailbox still will be residing in Azure Active Directory recycle bin for less than 30 days. Also, the mailbox is termed as soft-deleted if Azure active directory user account related with user mailbox has been hard deleted. Or, if user mailbox has been soft-deleted for more than 30 days, or the related Azure active directory user has been hard-deleted, the mailbox gets deleted forever.
You can delete Exchange Online mailboxes in two different ways:
The easiest method to delete a user-mailbox in Exchange Online is by using Office 365 admin center
If you delete a user account in Office 365, the related mailbox from Exchange Online gets deleted. And the user account in Office 365 gets listed in the Deleted Users page in Office 365 admin center. This user mailbox can be recovered within 30 days. After this time exceeds, it gets permanently deleted and cannot be recovered.
This is how you can delete user mailboxes in Office 365:
Similarly, you can delete user mailboxes one-by-one. After deletion, to stop paying for the license assigned to the deleted user-mailbox, you need to remove its license. To do this, go to Office 365 admin center. Then, navigate to Billing>Subscriptions; select the subscription and then choose Add/Remove licenses to delete the license and stop paying for it.
You can permanently delete Exchange Online user mailboxes using Windows PowerShell:
$UserCredential = Get-Credential
To view the user profiles residing in your deleted folder (as it resides in the deleted folder for 30 days period), run the following command:
Get-MsolUser – ReturnDeletedUsers
Remove-MsolUser -UserPrincipalName <mailbox identity> -RemoveFromRecycleBin
Old and outdated user mailboxes are always undesirable and should be properly disposed of. These two easy methods provide solutions to get rid of unwanted data. Although, if you want to back up your Exchange Online mailboxes before deleting them, trust Kernel Office 365 Backup & Restore tool. It is an advanced Office 365 Backup tool to back up Exchange/Office 365 mailboxes and import PST files to Office 365.