Should offline defrag be considered as one of the scheduled maintenance task for Exchange administrators? The short answer is going to be "No". The simple reason behind this, taking Exchange offline will cause "Outage" and if there is no space gain (white space, 30 percent usable space) there is no point of performing offline defragmentation at any cost.
Let me state this up front, those of you who are running enterprise version of Exchange should never perform offline defrag and cause outage, you need to create empty database and move user mailboxes
(In the night& off business hours) onto it and delete the old one contains white space. (Assuming you does have at least, one mail store available to achieve this goal.)
The process behind running offline defrags is that, exchange wont takes existing database and remove the white pages out the database and makes it ready to use. It Instead it copies used pages from old database and creates new database. When copy pages finishes it re-point the logs to the new database and it assigns nee signature to it.
How do we know if we need to perform offline defragmentation, the Exchange server's application logs "1221" will tell you how much white space (unusable)
Here is great article goes deep into 1221
Here is MS team blog goes deep into
Oz ozugurlu MVP (Exchange)
MCITP (EMA) , MCITP (EA ) MCITP(SA),
MCSE (M+,S+) MCDST, Security+, Server +,Project+