Here’s How to Fix It Fast
Ever received a “mailbox almost full” warning? It’s easy to overlook, but hitting your storage limit can lead to frustrating issues.Like not being able to send or receive emails right when you need to the most!
If your inbox is overflowing, don’t worry. You don’t have to buy extra storage just yet! There are quick and effective ways to free up space, keeping your Microsoft 365 mailbox running smoothly without extra costs.
Why Is My Mailbox Full?
Microsoft 365 mailboxes come with a storage limit, and every email you receive—especially those with attachments—takes up space. Here’s why your mailbox might be filling up:
- Large email attachments – A single email with a large attachment can take up as much space as 50 regular emails.
- Old emails piling up – If you rarely delete emails, years of messages may be clogging your storage.
- Deleted Items not being emptied – Many people forget that emails in the Deleted Items folder still take up space until permanently removed.
- Moving emails into folders doesn’t reduce storage – Organising emails into folders doesn’t actually free up any space. They’re still stored in your mailbox!
How Much Storage Do You Actually Have?
Most Microsoft 365 licences include an email service called Exchange Online Plan 1, which provides each user with a 50 GB mailbox. This is plenty for most users, but if you handle large attachments or high email volumes, it can fill up faster than expected.
If 50 GB isn’t enough, you can upgrade to Exchange Online Plan 2, which doubles your storage to 100 GB and adds advanced security and archiving features.
📊 Exchange Online Plan Comparison
| Feature | Plan 1 (Included with Most 365 Licences) | Plan 2 (Upgrade Available) |
|---|---|---|
| Mailbox Storage | 50 GB | 100 GB |
| Attachment Size Limit | 150 MB | 150 MB |
| In-Place Archive | ✅ | ✅ + Auto-expanding archive |
Good to know: If your mailbox is constantly full, an upgrade to Plan 2 may be cheaper than increasing storage on your entire Microsoft 365 plan.
How to Free Up Space in Your Mailbox (Without Buying More Storage!)
Before you consider upgrading, try these simple but effective housekeeping steps first.
1. Sort Emails by Size & Delete the Biggest Ones
Your largest emails are the easiest way to quickly free up space. Here’s how to find them:
✅ Open Outlook and go to any folder you want to clean up
✅ Click on Sort by > Size.
✅ Look for emails with large attachments (these can be up to 50MB each!).
✅ Delete emails you no longer need, but save important attachments to OneDrive or your computer first.
Pro Tip: If you don’t want to delete an email but need space, download the attachment and remove it from the email instead!
2. Use the Mailbox Cleanup Tool
Microsoft Outlook has a built-in Mailbox Cleanup tool that makes it easy to see what’s taking up space and remove old, unnecessary emails.
Here’s how to use it:
1️⃣ Click File (top left of Outlook).
2️⃣ Scroll down and click Tools.
3️⃣ Select Mailbox Cleanup.
4️⃣ Choose options to find large emails, old emails, or duplicates and delete them.
Bonus Tip: You can use the “Find items older than X days” feature to clear out emails you no longer need!
3. Empty Your Deleted Items Folder
Many people don’t realise that Deleted Items still take up storage! Your deleted emails sit in this folder until permanently removed, continuing to use valuable space.
To free up space:
1️⃣ Open Outlook and find the Deleted Items folder.
2️⃣ Right-click on it and select Empty Folder.
3️⃣ Confirm deletion when prompted.
💡 Want to automate this?
Go to File > Options > Advanced, then under Outlook Start and Exit, tick the option to empty the Deleted Items folder when Outlook closes.
Still Need More Space? Consider an Upgrade
If you’ve tried all the steps above but still need more storage, here are your options:
💾 Archive Old Emails – Move old emails to an archive file (.PST) on your computer.
📤 Use OneDrive for Attachments – Instead of emailing large files, upload them to OneDrive and send a link instead.
📦 Upgrade Your Microsoft 365 Plan – If your mailbox is full even after cleanup, upgrading to Exchange Online Plan 2 will double your storage to 100 GB.
Should you upgrade to Exchange Online Plan 2?
✔️ If 50 GB isn’t enough and you want a simple, cost-effective upgrade, it’s the best option.
✔️ If you need advanced security features like Data Loss Prevention (DLP) and auto-expanding archives, Plan 2 is the way to go.
🔍 Not sure what’s best for you? Contact Nxt Gen IT and we can help assess your storage needs and recommend the best solution.
Too Busy? Let Us Handle It for You!
Don’t have time to go through your inbox? We can remotely clean up your mailbox for you!
📞 Call us at 0333 231 1000, and we’ll get your email running smoothly again, without you lifting a finger.
✅ Fast, stress-free service
✅ No risk of losing important emails
✅ Expert recommendations to prevent future issues
👉 Don’t wait until your inbox stops working—fix it today!
Ben helps growing businesses turn technology into a driver of performance instead of a barrier. At Nxt Gen IT he works with SME leaders, recruiters, and fast-scaling teams to design solutions that improve reliability, strengthen security, and unlock growth.
With a background in email deliverability and cloud systems, Ben specialises in making sure businesses communicate effectively, keep data safe, and get the most from Microsoft 365. His experience spans solution design, managed IT services, and virtual CIO support, always with a focus on practical outcomes that reduce headaches for business owners.
Ben has supported organisations across the UK, from recruitment agencies struggling with inbox placement to SaaS firms scaling fast, and SMEs needing a trusted partner for their IT. He believes tech is never the end goal: growth is. His role is to make sure technology never gets in the way of it.