Managing mailbox storage with Exchange 2010, Part 3

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In the previous part one and two of this series, I’ve discussed using PSTs, Exchange Personal (on-premises) and On-line Archiving as well as third party solutions. In this last post I will discuss the use of Retention Policies and Mailbox quota’s in order to manage storage usage. As a bonus I will shortly discuss improvements in Exchange/Outlook 2013.

Retention Policies

RetentionPolicyThe basic Messaging Records Management functionality behind Retention Policies isn’t actually that new. In Exchange 2000 and 2003 you could configure Recipient Policies and in Exchange 2007 you had Managed folder Content Settings.

All of them regulate the retention of mail items (and since SP2RU4 Exchange 2010 also managed calendar and tasks items) of the complete mailbox or certain specific folders within a users mailbox. You can delete it with recovery, delete it without recovery or move it to the Archive Mailbox (if the users has one). For instance, a 90 day old mail in Deleted Items or even Sent Items could have lost it’s worth and the cost of keeping it in the mailbox too high, but the user could keep forgetting to clean up or the mailbox is shared and hasn’t got a main user which keeps it manually neat and clean. As it is processed server side (on the Mailbox role), the effect is client independent.

In Exchange 2010 you can give users the option of tagging specific (sub) folders and mail items, so that these objects will have another retention than the default setting. You can allow users set No Archive/No Delete tags or increase (or lowering) the retention period of the item (via a Personal Tag). But the admin still has control on which tags are included in a Retention Policy which is in it’s turn appointed to a mailbox and default folders aren't configurable for users. However, usage of (non default) Personal Tags in a policy requires an Exchange Enterprise CAL, other cases only an Exchange Standard CAL is required.

Personally I use them for certain mailing lists, like all my LinkedIn notification mails. Their use expires quickly (because it’s just a notification, thus I've changed the folder retention period from default (never delete) to 30 days after which the mails are deleted.

A very helpful tool, which can benefit admins a lot because it lowers resources. But it is also helpful users by keeping some folders lean and mean, which reduces the risk of reaching quota limitations and it helps keeping only items that really matter.

Combined with the Personal Archive or Online Archive, an admin or an user can control when items are moved to the archive mailbox rather than just deleted.

Too bad the policies only work on retention and not on other criteria like Categories, and that it processes the whole mail item and not just the attachment for instance.


  • Admin has control and is able to give users (some) control
  • Actions (such as deletions) are performed automatically on the Mailbox server, no client side rules thus also valid for other clients than Outlook
  • Different policies with different Policy Tags can be implemented on a per mailbox basis
  • No added license cost for default settings, it is included in the Standard Exchange CAL
  • Can be combined with Archive Mailbox


  • Only on retention, no specific rules on mail items with attachments for instance.
  • Users need to be instructed about the admin settings in order to prevent accidental deletions
  • Has a bit of a learning curve
  • Mailboxes with customized retention polices with Personal Tags, require an Exchange Enterprise CAL

Mailbox quota’s

OutlookQuotaAnd last but not least, Mailbox Quota’s. These are settings on a database or mailbox level (which overrides the database setting) and entail a warning, prevent sending and ultimately prevent sending & receiving mail threshold. It is actually on of the things you use to correctly size your mailbox server role.

But how does this help you? Well, even if you have sized your server by the book, it doesn’t mean your users will adhere to your expectations and sometimes faulty clients or other reasons can overflow a mailbox. In extreme cases it could use all available disk space and cause Exchange to dismount the database. Which leads to unhappy users.

Usually I tend to configure the quotas on the database level and have several databases (maximum of five on Exchange 2010 Standard) with different quota levels. This is an easy way to make it easy on administrators or even your service desk to quickly raise someone’s quota by simply moving the mailbox to another database (which isn’t much of a problem anymore with Exchange 2010 as the mailbox is only shortly locked at the end of the move).

With Exchange standard you can have up to five databases, so you can have five different quota settings. Four if you still need a Public Folder database. I tend to call this Mailbox Quota Tiering. It is a bit more tricky to project each DB’s maximum size, so capacity management in one form or another will be important. Furthermore, you’ll need management backing for the different quota settings and a clear process for moving users from one quota tier to another.

However, if you have a Database Availability Group and several Mailbox servers this could result in an less than optimal distribution of databases. Therefore in those cases I revert to specific mailbox quota’s per mailbox, when the database default (the same on all DB’s) isn’t sufficient. Management is more cumbersome, using scripts is probably a good way to reduce this.

In my experience having a Mailbox Quota Tiering system offers you and/or management a tool for controlling quota’s and thus storage use. I’ve seen too much issues rise from suddenly imposed quota’s and/or clean up requests due to rapidly shrining free storage space. Having several quota’s also offers users an alternative than immediate cleaning, which is more service oriented. This could be even more important than the technical benefits.


  • When properly sized, quota’s help preventing storage filling up due to an issue or normal growth
  • When using DB specific quota’s, one only needs to remember to place the mailbox in the correct DB
  • Having a clear quota policy in place helps prevent unpleasant surprises for users, management and admins


  • When using mailbox specific quota’s, additional administrative effort is required
  • It’s no guarantee storage won’t fill up, storage space monitoring is still required
  • You’ll need backing from management for the specific quota settings and a process in place for moving users from one tier into another

Outlook 2013

Outlook2013Since I planned this series of posts, Outlook 2013 has been released. One feature that could be helpful is the Sync slider or the OST slider. As Exchange 2013 raised the supported mailbox size from 25GB in Exchange 2010 to 100GB an issue can occur when the computer with Outlook 2013 in Cached mode does not have the space required to store this amount of data. Especially laptops and slates with SSD prefer speed over storage space. However, it does not manage the amount of storage needed on the Exchange server but I felt it was worth mentioning as it does have effect on local computers storage.

The Outlook 2013 OST Slider

The OST slider (see image) is a way to limit the amount of data stored on the local drive by only downloading the last 2 or x amount of months. You can give users the control over it or configure it via Office 2013 Group Policies. When an item isn’t stored within the OST, Outlook needs a connection to the Exchange server. You could say it is comparable with the Personal Archive functionality, however you do not need an Exchange Enterprise CAL for this and you can differentiate the OST Slider settings per computer. You do need an Office 2013 license obviously.

This feature can be another approach to limit the amount of data stored locally and thus can be a competitor of the Personal Archive. Especially when you have Office licenses with Software Assurance the costs are possibly less than when you have to purchase said CAL. If needed you could combine it, but the limitations of the Personal Archive are then still present.


  • Works with Exchange 2007, 2010 and 2013
  • User control or admin control on OST slider
  • Data can be stored in a single mailbox, no need for Archive


  • Needs Office 2013 (with Outlook)
  • Only time based
  • Only tackles the amount of storage needed on client computers, not on the Exchange server

Overall Conclusion

Well, we discussed PSTs, Personal/Online Archive mailboxes, Third Party Archiving solutions, Retention Policies, Mailbox quota’s and the new Outlook 2013 OST Slider. As you can see there are several approaches to manage the amount of storage necessary for Exchange and Outlook. Except for perhaps PSTs (“Kill it with fire!”), there isn’t a complete answer.

As an admin and organization, you still have to decide which technology suits your needs and wants the best. It could be just one solution or a combination of some or all of them. I hope I gave you some pointers that will make it more easy to decide which is the best fit for you.

This concludes this series of blog posts on managing mailbox storage with Exchange 2010. Please note that some techniques are valid for other versions of Exchange, but my main focus was Exchange 2010.


Managing mailbox storage use in Exchange 2010, Part 1
Managing mailbox storage use in Exchange 2010, Part 2

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