In our Exchange Server environment, we've set the Exchange servers' deleted item retention period lifetime to 45 days. We're running out of space on one server. Will reducing the retention period lifetime free any disk space?
Yes. When you change the retention period lifetime, Exchange System Manager (ESM) writes that change to Active Directory (AD), and the affected server (or servers) will pick up the change the next time they refresh their configuration from the Configuration naming context (NC). However, the change won't take effect until the next time the target server starts its online maintenance period, which usually happens overnight. At that time, the server will purge any messages that are now older than the new retention period lifetime, and the space those messages formerly occupied will be returned to the database white-space pool. Of course, changing the retention period lifetime won't reduce the amount of disk space that the database itself uses; only an offline defragmentation will reduce the database. However, the Information Store (IS) can reuse those reclaimed pages without causing the database to grow further.