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Office 365 Mailbox Size Troubleshooting


Microsoft Office 365 includes a large amount of mailbox storage per user, especially relative to legacy and prior-generation email systems. However, you may still find yourself running low on available mailbox space.
 Outlook has built-in tools to search and clean up old or large content. However, this is often undesirable:
  • time-consuming
  • requires deleting content that you would prefer to keep
Greenloop can help with this! the good news is, Office 365 has some easily accessible options for increasing your available storage and automating archive of old emails. These may be included in your existing Office 365 subscription (and just need to be enabled) or can be added for a small monthly cost.

How to check your current mailbox size and size limit

Follow the steps below to determine your current mailbox size and size limit.
Modern versions of Outlook are designed to work well with large mailboxes and unless your mailbox size is approaching the limit (80%+ is usually a good rule), you shouldn’t need to take any action.
In the Outlook ribbon, click the File menu:
You should see a mailbox size indicator as shown below:
In this particular case, there is plenty of free space and no further action is needed.

Increase your available storage (mailbox size)

Increasing your mailbox size, if possible, is GreenLoop’s first recommendation whenever encountering size limitations. This keeps all of your mail in the same mailbox structure you’re used to and increases how much space Microsoft allows.
Most Office 365 licenses currently have a 50 GB limit. You can easily increase this to 100 GB by adding an Exchange Online Plan 2 license to your mailbox (current monthly cost $8/user). Please let us know if you would like to increase your size limit by adding this license.
Note: Microsoft does not allow primary mailboxes to be over 100 GB. If you require more storage, you’ll need to use the Exchange Online Archive (keep reading!).

Automate archiving of old emails to the Online Archive

All Office 365 email accounts include the capability to enable an Online Archive mailbox. Depending on the license you have, this may give you an additional 50 GB of storage, or be virtually unlimited (1.5 TB).
The Online Archive acts like a second, nearly-invisible mailbox. Once enabled, Exchange Online automatically moves old emails into your Online Archive based on rules at the organizational level.
For most organizations, the default rule is a 2-year-move-to-archive.
Additional "retention tags" (rules) can be created and applied to individual items, or folders. 
Additional policies can be created, applying different default rules to individual mailboxes if needed.

Enabling your Online Archive

Contact GreenLoop to request that Online Archive be enabled for your account(s), or to find out what your default archiving rules are, or what other retention tags exist.

Finding your Online Archive

Your Online Archive is fully searchable in Outlook on the Web and in supported, modern versions of the Outlook client.
In Outlook for Windows, your Online Archive appears as a parallel set of folders to your primary mailbox folders, as shown below:
In Outlook for Mac, it will show up as a “Personal Archive”:
Online archive in Outlook for Mac

Next steps

If you’ve done both of the items above (increased primary mailbox size, enabled Online Archiving) and you’re still running low on disk space, GreenLoop can still help! Reach out to us for help creating a custom Message Retention Management policy for individual mailboxes that need it.

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