If you have recently deleted an AD user account and ‘marked mailbox for deletion’ and want to immediately purge that mailbox you will find out that the option is greyed out. This is because there is a 30 day retention period in which exchange has marked the mailbox for deletion but has not actually removed it.
To force a purge:
1. Open Exchange System Manager
2. Browse to Administrative Group > First Administrative Group > Servers > yourserver > First Storage Group > Mailbox Store (yourserver) > Mailboxes.
3. Right click on Mailboxes in the left window pane and choose “Run Cleanup Agent”
4. Over in the right window pane you will see a red X over the mailbox you want to purge.
5. You can now right click on the mailbox and choose purge (or reconnect).
