Exchange Archives

archivesWhen it comes to Exchange, one of the confusing things for customers is the Exchange Archive feature – especially for customers coming from an existing 3rd party archiving solution.  When I work with customers who are upgrading to a newer on-premises version, or Exchange Online, and have a current archiving system in place, the first thing I ask is what is the current solution used for? Archives are used for either compliance reasons (e.g. retention, records, litigation, legal requirements, etc.) or to extend mailbox capacity (e.g. provide large mailboxes by using lower cost storage). Occasionally, the archive may serve both functions.

When planning for the new end-state design – the question is what do to?  Most customers assume they should just deploy Exchange Online archiving.  This post will give some reasons to reconsider that decision.  [Spoiler] Exchange’s online archive feature has nothing to do with compliance.

Exchange Archive: The Origin Story

in the beginning

The origin of the archive feature (the name has changed many times over the years) was first introduced in Exchange 2010.  One of the goals in Exchange 2010 was to provide support for large mailboxes (which in retrospect were not all that large compared to Office 365 today!)  The main problem was that Outlook 2010’s cached mode would cache the (whole) mailbox, so rather than rely on a change to the Outlook client, Exchange added the archive feature – which is an extention to your mailbox that would not be cached.  If you deployed an archive, you could enjoy a very large mailbox, and not need to cache all your mail. For on-premises deployements, you could even put the archive on seperate storage, or even seperate servers. This was great since really large mailboxes take a very long time on the initial download or if you had to recreate your profile (which for many customers is a standard troubleshooting step).  Also, many laptops were very limited on drive space.

What about compliance features and the online archive?  The online archive actually did not bring any new compliance features with it.  All the compliance features apply to the mailbox – the whole mailbox – not just the primary mailbox.  Any retention or legal hold applied to the person apply to both the primary and the archive, or just the primary mailbox if an archive was not used.  In other words – having an archive added no additional compliance capabilies.  This was true in Exchange 2010, and is still true today.

Why Deploy an Online Archive?

If we don’t get additional features, then why deploy an online archive?

  1. You exceed the capacity of your primary mailbox storage (currently at the time of writing this, Office 365 E3 includes a 100GB primary mailbox)
  2. You have Outlook 2010 (or older) clients and want to have large mailboxes. Given Outlook 2010 is out of support, customers should be doing everything possible to upgrade.

If you have deployed an archive product for addressing mailbox capacity issues, then I strongly recommend that you do not deploy the online archive by default. Why not?

  • Not all mail clients can access the online archive
  • Mobile clients cannot search the online archive
  • It more complex and can be confusing to people

In this scenario, just use a large primary mailbox as Outlook 2013 or newer have the option of setting the amount (based on time) of cached content.  This cache setting effectively works just like having the archive (since content not in your cache is only available while online).


If you deployed an archive product to meet compliance or records management needs, consider using the native Exchange features such as hold, retention, MRM, and labels.  Keeping all email within Exchange versus using an external archive product lets you easily perform content and eDiscovery searches.  Also, its much easier to manage your data lifecycle with the mail being on one solution.  I’ll reiterate – these compliance and records features work in Exchange regardless if you deploy the Exchange online archive or not.  In other words, you could retire your external archive, only use a primary mailbox, and enable retention policies to continue providing an immutable copy of the person’s mailbox data.

A very common scenario for customers as they move to Office 365 is to ingest all their 3rd party archive data, and PST (local / personal archives) in to Office 365.  Given this could be a lot of data, exceeding the 100GB limit, customer migrate this data directly into the online archive.  Exchange Online does offer an unlimited, auto-expanding archive.  Note that for migrations, the archive expansion takes time – so you cannot just import everything at once.  Once the content is in Exchange, retention policies can be applied to all content to start to control your enterprise data and limit risk exposure.

As long as the archive on the source system corresponds to a mailbox, this type of migration is straight forward.  If your archive solution is for journaled mail, typically the archive is not associated to specific mailboxes.  This is much harder to ingest in to Exchange, and a better strategy could be to just sunset the journal solution (let it age out) and moving forward implement retention and the other compliance features mentioned above.  A nice benefit of using retention over journaling is journaling only captured email sent and received.  There are scenarios where people shared folders to trade messages, which never actually go through transport!

Hopefully this sheds some light and helps you decide when to use Exchange online archives, how they work, and the benefits / drawbacks if you do plan to use them.