Primary Mailbox – this is a users’ primary mailbox where all mail is delivered to and sent from. When using Outlook in cached mode, there is an OST file available to be saved on the local device. The size of the OST file can be controlled within Outlook based on a time stamp.
Online Archive – this is an ‘online archive mailbox’. The word online is a little misleading as it describes the fact that the client access to this mailbox must be online or connected to either an Exchange Online (EXO) archive mailbox or to an Exchange on premises archive mailbox to access the messaging content. In other words, there is no OST file available for the client to use while ‘offline’ or not connected to an Exchange environment.
In-place Hold and Litigation hold – these are the options to stop data from being deleted from a mailbox. Even if the end user: deletes a message from the inbox, deletes a message from the deleted items, and deletes a message from the ‘recover from deleted items’ view, Exchange can retain this information while not impacting the users’ mailbox quota. Though, there is a ‘recoverable items folder’ quota that does have a current 100GB limit in EXO and a 2TB hard limit for Exchange on premises environments.
Auto-split – is the backend process that allows an archive mailbox or public folder to expand automatically when they reach a certain size. This process can allow unlimited growth of data. However, this auto-split process is ONLY available in an EXO archive mailbox (not Exchange on premises) and EXO public folders. This process is NOT available for a primary mailbox.
Unlimited Online Archiving – is yet another new option for administrators to leverage keeping as much mailbox content as you desire. This unlimited archiving leverages the auto-split process allowing an auto-expanding, unlimited storage experience for O365 customers. The Math: 150kb average message size; 100GB of storage; is around 650,000 messages (2TB of storage is over 13 million messages).
Retention Policies – have the ability to either move messages from a primary mailbox to an online archive mailbox or delete mailbox items from either the primary mailbox or the online archive mailbox. If there is a retention policy applied to the Recoverable Items folder, the background process will also move those messages to the online archive mailbox of that user, if an online archive mailbox exists.
Preservation Policy – this is a new option for customers in O365 with industry regulations or internal policies needing to preserve content for a specific period. Data retention is available for: Exchange, SharePoint, and Public Folders. This preservation policy leverages the Exchange in-place hold process for mailboxes.
O365 Plans – another item to be aware of is which O365 plan you are using and which Exchange Online Service is setup in your tenant. There are several options and within those options, are specific Exchange Online plans. Depending on the O365 plan you have, would indicate which Exchange plan (1 or 2) you have access to, which then could limit the primary mailboxes to 50 GB (Plan 1) or allow Unlimited Storage (Plan 2) depending on your how your tenant is licensed.
Administrators call to action
Now that you’ve read this far, you should be able to see the predictable ending to this saga. If not, here is the story. To this point, we have defined several topics and gathered the pieces of the puzzle, we can now: lay them out on the table, put them together, and then realize the big picture.
If you want to retain messaging content for as long as you want and NOT ever run out of space within EXO, you will need to: consume an Exchange Plan 2 in your tenant, implement an online archive mailbox – with auto-expanding feature enabled, deploy retention policies, and possibly setup a preservation policy. If you don’t, you may end up running out of space in a primary mailbox before your legal required time lapses. I like to strategize when I can, and this little proactive planning for the potential need to keep as much data as possible for every mailbox in an environment for as long as you want and never run out of space, is what we’re talking about.
Like I said, I love the cloud, especially this option to retain unlimited data forever! With some proper preparation, you too will be able to implement these options to help your company meet all compliance regulatory conditions and not run out of primary mailbox storage.
Mike