A couple of recent questions about the exact nature of archive mailboxes prompted consideration of the topic. It’s the nature of software deployment that the finer points of technology are left until the basics are covered and an increase in interest in archive mailboxes is possibly due to the number of Exchange 2010 deployments that have reached the point where they have completed the migration off a previous version and are now in a pure Exchange 2010 environment. Or it might just be that curious minds have started to think about archive mailboxes at a level past the perspective of “wow, I can stuff lots of stuff into an archive mailbox.” (See also, "Exchange 2010 Archive Mailbox Sizing and Scaling," October 2011).
Here are the top six things to know about archive mailboxes.
First, Exchange on-premises customers must purchase enterprise CALs if they want to use archive mailboxes and the other retention features built into Exchange 2010. An enterprise CAL is accretive to the standard CAL that you must have to use the basic features of Exchange.
Users who hold Office 365 Plan P and Plan E subscriptions automatically have access to online archives. Plan K (kiosk) subscribers will be able to add archive capability soon.
Second, no one receives an archive mailbox by default. An administrator has to specifically assign an archive when the mailbox is created or enable the archive for mailboxes that already exist. For example, running the command
Enable-Mailbox -Identity "Tony Redmond" -Archive
enables an archive for my mailbox. In this case I don’t pass a value to the ArchiveDatabase parameter so the Enable-Mailbox cmdlet will create the archive in the same database as the primary. Note that Exchange applies the default archive and retention policy to mailboxes when you enable them with an archive. This can have some unwanted side-effects for users so it’s worth doing some up-front planning before you start to enable any mailbox.
Third, archive mailboxes don’t have to be in the same database as the primary mailboxes. That restriction was lifted in Exchange 2010 SP1. You can enable or move an archive as follows:
- In the same database as the primary mailbox
- In a different on-premises mailbox database (Exchange can select a database automatically for you if you like)
- In a database in an Office 365 tenant domain (if you run a hybrid on-premises/cloud environment)
Fourth, archive mailboxes are very similar to standard mailboxes in the way that they are represented within a mailbox database. The archive is connected to the user’s primary mailbox by two properties that tell Exchange how to find the mailbox. The first is ArchiveGUID and the second is ArchiveDatabase. ArchiveGUID is a 32-bit unique identifier that identifies the location of the archive mailbox within the database pointed to in the ArchiveDatabase property. ArchiveDatabase will be blank if the archive is in the same database as the primary. To see all the archive properties for a mailbox, run the Get-Mailbox cmdlet and extract the relevant properties. For example:
Get-Mailbox -Identity ‘Tony Redmond' | Format-Table Archive*
Fifth, while internally the contents of an archive mailbox are very similar to that of a primary database, there are a number of major practical differences that you might encounter. These are:
- The set of default folders (Inbox, Sent Items, Calendar, Contacts, Junk Mail, etc.) that Exchange creates automatically in the primary mailbox are not created in an archive. The Deleted Items folder is the only default folder that is created when the archive mailbox is enabled.
- Exchange applies very different limits to the archive mailbox than it does to the primary. The whole point of an online archive is to act as a repository so the default limits are usually much higher (initially, Exchange 2010 assigned unlimited quotas) than used for primary mailboxes. The default limit assigned by Exchange 2010 SP1 for on-premises mailboxes is 50GB.
- Outlook will never synchronize content from an archive mailbox into its local cache (OST file).
- Exchange will never deliver new Incoming mail to an archive mailbox. However, you can create a rule to move new mail to a folder in an archive mailbox. Likewise, there’s no way to send new messages from an archive mailbox as Exchange will always use the primary mailbox for this purpose.
- Only Outlook and Outlook Web App clients can access archive mailboxes. They are invisible to POP3 and IMAP4 clients as these protocols don’t incorporate the concept of a separate archive mailbox and also invisible to ActiveSync mobile clients as ActiveSync has not yet been upgraded to expose archive mailboxes.
Sixth, although you can use the standard planning methodologies to figure out how many archive databases you need, where they should be positioned, and whether it makes sense to separate archives away from primary mailboxes, you have to remember that the biggest single difference between archive and primary mailboxes is that an archive mailbox is essentially passive for most of the time. A primary mailbox is like the Duracell bunny on steroids because it’s usually busy during the working day, processing new messages, running rules, sending outgoing mail, and responding to user requests. The busiest that an archive mailbox ever gets is when the Managed Folder Assistant moves expired messages from the primary into the archive to comply with a retention policy. Apart from that it’ll receive intermittent access as the user gradually forgets what’s held in their archive. After all, this happens with paper archives so why shouldn’t it happen with electronic archives?
Those wanting more information about archive mailboxes might like to consult pages 976 through 988 of Microsoft Exchange Server 2010 Inside Out - just in case there’s something good in those pages.
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