How to increase your mailbox storage | Identify Mailbox is Full

As MSPs, we still get plenty of helpdesk tickets which can be summarized as the following:

• My email is running very slow
• I am unable to send or receive email
• I am getting warning messages that my inbox is almost full

Many of our end-users show significant signs of hoarding where they don’t delete any emails and worry about not being able to access emails over 10+ years old. In this article, I am going to show you some proactive practices to understand when mailboxes across your environments are over 90% full and some strategies that you can use to increase mailbox storage to 1.5tb on a single mailbox WITHOUT purchasing additional licensing.

Legacy Practices of Managing Full Inboxes#

Trying to get users to delete old items: Over 50% of the time this does not go anywhere as they are unmoving to deleting old emails.

PST Files: If you’ve been using Outlook for years, you might have accumulated PST files—those massive, clunky files that store old emails on your local computer. While they were useful back in the day, they’re a headache to manage and can cause problems with your mailbox performance.

Moving to Exchange Online Plan 2: This has been a common practice for many years given that EOP2 licensing gets us a 100GB mailbox, a bump from 50GB that comes with the business plans.

Identifying Full Mailboxes#

There are different ways you could identify full mailboxes within your organization, but I am going to show you how to view these within the Microsoft 365 admin center, along with a 3rd party tool that I build to help you become more proactive when mailboxes are almost full.

Microsoft 365 Admin CenterWithin the admin center, you can go to Reports>Usage>Exchange>Mailbox Usage and see a list of mailboxes and if they are close to “quota” which is their effective mailboxes size

CloudCapsule I built a tool called CloudCapsule which performs and automated security assessment against your Microsoft 365 environment and also identifies any mailboxes over 90% full with storage. This also includes a flag to show if Online Archiving is enabled for the mailbox which we will get to later in the blog. Run a free assessment today to see how this looks in your environment.

Learn More (opens in new tab)

Best Practices to Remediate#

Encourage the user to clean up their mailbox using some of the features such as the following:

• Use the storage feature to clean up full folders such as your Junk mail or deleted items. (Settings (Top Right Corner)>General>Storage)
• Use the “Sweep” Feature to begin to move items form your inbox that are recurring to archive or deleted Organize your inbox with Archive, Sweep, and other tools in Outlook on the web – Microsoft Support (opens in new tab)
• Identify if older mail can be deleted. This is usually where we get pushback but try to identify if we can put a retention policy in place that would allow us to delete email 5+ years old. Some companies need to retain records legally for longer so just be cognizant of that. Assign and view retention policies on email messages – Microsoft Support (opens in new tab)

Admin Discovery:

• Look for any litigation or eDiscovery cases against the mailbox that could be retaining items longer: How to identify the hold on an Exchange Online mailbox | Microsoft Learn (opens in new tab)
• Identify the retention policy being applied to a user Apply a retention policy to mailboxes in Exchange Online | Microsoft Learn (opens in new tab)
  • Retention tags and retention policies in Exchange Online | Microsoft Learn (opens in new tab)

Enable Arching on the mailbox

When you enable and online archive for a mailbox, two major events happen:

• The user gets another 50gb (or more depending on licensing) archive storage container
• Unless another policy has been explicitly applied, the default retention tags will move any emails over 2+ years old into this archive bucket.

For the user, its important to note that this is not deleting any email, its simply moving older items to a new bucket. After you activate the archive, a new folder will appear in their outlook environment:

See the instructions here for enabling an online archive for a mailbox: Enable archive mailboxes for Microsoft 365 | Microsoft Learn (opens in new tab)

Enabling Auto-expanding ArchiveNow this is where the juicy detail come into play that many of us do not know about. If you are leveraging Microsoft 365 Business Premium, you can actually use a feature called auto-expanding archive to allow the archive mailbox to continually get more storage up to 1.5tb. Here are some of the other licensing that allows for this:

If you are not on BP and are still considering going the EOP2 route to pair with a Business Standard consider that BP is 22/u/m and the bundle of EOP2 + Standard is $20.50 ($8 + $12.50). Not a whole lot of difference for 1.5tb vs an additional 50gb and a ton of security features. The asterisk to this is if the user is hard insisting on not moving older email to the archive. 

Storage Limits in 365: Exchange Online limits – Service Descriptions | Microsoft Learn (opens in new tab)

Licenses for Email Archiving: Microsoft 365 guidance for security & compliance – Service Descriptions | Microsoft Learn (opens in new tab)

You can turn on auto-expanding archive org wide or on individual mailboxes using PowerShell. This is the only supported method to turn this on at the time of this writing. See the instructions for turning it on here: Enable auto-expanding archiving | Microsoft Learn (opens in new tab)

Don’t Forget to Protect Your Emails with Third-Party Backup#

While Microsoft 365 offers robust email management and archiving features, it’s also a good idea to consider a third-party backup solution. This extra layer of protection ensures that your emails are backed up and easily recoverable in case of accidental deletion or data corruption. It’s the digital equivalent of keeping a copy of important documents in a safe place. This could also be used as a tactic for getting users to delete more of their older mail, knowing that it is recoverable via a restore of a backup. There are certainly plenty of 3rd part backup solutions out there but these are my favorite:

• Acronis:Cybersecurity & Data Protection Solutions – Acronis (opens in new tab)
• Dropsuite: Office 365 Backup, Archive & Recovery Solutions | Dropsuite (opens in new tab)

Conclusion#

Get ahead of users reaching out about their mailbox being fullwidth these solutions. Always encourage best practices of maintaining proper email hyenine but after these solutions in mind to accommodate for additional storage.