Each Microsoft Exchange mailbox by mailbox and Active Directory user account data stored in the Exchange mailbox database components. All configuration data is stored in the Exchange mailbox attributes of Active Directory user object. Mailbox database contains the mail data associated with a user account mailbox. The following figure shows the various components of the mailbox.
NOTE: Disabling the default mailbox data retention in exchange for 30 days.
Deleted directly in AD domain account, then the mail will be deleted, and can not find the mailbox is deleted in "Connection mailbox" option. Want to restore a mailbox can only be restored first AD domain accounts, email accounts will automatically revert back.
Delete email account on the exchange then the AD account will be deleted, but can be found in the mailbox is deleted "even the amount of mail" option. If you can not restore the AD account and want to restore mailbox data, you can mount the mailbox data to other AD accounts.
Several common situations:
First, disable only the Mailbox role, there is AD account recovery:
1. Open the "ECP", select "Connect mailbox."
2. Click on the top left corner "Connect":
3. Select the Mailbox role is to be restored, and the data is preserved.
Second, how the AD account for mailbox role recover accidentally deleted (AD Recycle Bin is enabled).
1, the AD account deletion:
2, open "AD Management Center" accounts for the reduction, as shown below:
3, after reduction mail account also automatically restored.
Third, the deleted mailbox to connect to other AD accounts.
1, select "Connect mailbox." 
2, select "Disable mailboxes." 
3, before AD account was deleted, display connected to other accounts (other accounts without the need to enable the Mailbox role), click on "I want to choose another account." 
4, an alternate user. 
5, the data will be restored to other accounts.
Fourth, after tests found, delete the domain account directly in AD, will not lead to "Connect Mailbox" option to retrieve mail via ECP-, can not be restored at this time as AD account, you can connect to another mailbox database AD accounts.
1, delete "A" account in AD.
2, in a new AD "A1" domain accounts. 
3, using the "Connect-Mailbox -Identity" A " -Database" edb02 "-User" A1 "-Alias A" AD command and connected to the mailbox. 
4, you can see to the A1 e-mail account in the ECP. 
5, using the A1 account login owa can see the data retained.
* If the objection, I would like him to guide!