View source for Exchange Archiving Strategies

Now it is certainly possible to have Exchange do its own archiving. You can set up a journaling mailbox or hold to hang on to everything as certain laws demand. If you have to keep messages for 10 years and average user may end up have hundreads of thousands of messages consuming tens of gigabytes of storage. And that is just the average user, a power user could consume far more. Can you imagine the drag on your Exchange server trying to handle all of that for thousands of users?

You could create a policy to move messages into an archive database, but since it is still connected directly to Exchange it will still be a load on the system. However there are going to be "interactions" between the holds and policies moving things to the archive database that may not allow them to be successful. 

==Exchange Archiving With Retain==
This is where Retain comes in. Retain offloads all the messages so that Exchange can concentrate on delivering messages rather then storing them.

The typical Retain setup does not do a true archive. The customer sets up a Retain server points it at the email server and has it do a dredge every night.

For example, a message can come to a user, the user can read it, move it to the trash, and delete the trash. Has the message been removed from disk yet? No, it has not. It is moved to the Recoverable Items area of the database, where it resides for 14 days by default before being deleted. A user can undelete the message from Recoverable Items. However, they can also purge their Recoverable Items, which would remove them from the disk, not allowing Retain to dredge the message before it is deleted forever. 

Unlike GroupWise, Exchange does not have message level retention abilities. So to make sure our customers are able to make proper archives there are some additional steps that need to be taken. 

==Journaling Mailbox==
Microsoft has recommended setting up a Journaling Mailbox if all messages are to be saved, but has been moving away from that stance lately. There is a very large downside with this technique. If the Journaling Mailbox becomes too large, ~100GB (with various settings maximized) though it will be smaller in default systems, Exchange becomes unable to serve the messages so Retain can archive and delete them. This may work in small systems or in limited circumstances, but for the most part it is not the recommended technique for Retain. 
*Exchange Journaling Mailbox Recommendations [http://support.gwava.com/kb/?View=entry&EntryID=2300]

==In-Place and Litigation Holds==
A more effective means of archiving messages in a large environment is to set up In-Place and Litigation Holds. These holds keep items from being removed from the Recoverable Items folder for a limited time.
*Exchange Archiving with In-Place Hold [http://support.gwava.com/kb/?View=entry&EntryID=2406]

A hold will keep the message in the Recoverable Items folder until the hold is released.

A good strategy for archiving is to create a rolling in-place hold so Retain has a day or two to successfully archive the messages, since Exchange doesn't have a message level flag to specify if a message has been archived or not you want to leave a little extra time to make sure Retain has a fair chance to archive.

A better strategy is to maintain the hold for 14-90 days, which will provide plenty of time to discover archiving errors and resolving them before data is potentially lost. 

If users are going into Retain for past messages it is a good idea to have Retain wait to archive say 7-14 days so the messages are in their proper folders.

==Office365==
Exchange and Office365 run maintenance every night between 1-5AM. You will want to schedule your archive jobs to run at times to avoid the maintenance window. For an initial archive dredge that will be impossible because it will take days or weeks, so expect connection errors.
Because of this it makes sense to run archive jobs during the day or at the least as close to the end of day as possible. It is simple enough to find the average duration a job takes and then make sure to start that far before the maintenance window.