Outlook Mailbox Size not reducing after Deleting Emails! – [SOLVED 2025]

Microsoft Outlook is one of the widely used email client application by all individuals and organizations. But many times, users end up encountering errors i.e. “Outlook Mailbox full”, “Outlook mailbox size not reducing after deleting emails” or, “mailbox is full, you cannot send/receive messages”. The problem creates challenges for users as it lowers the performance of Outlook and prevents data storage.

In the article, we will discuss the cause behind the error, provide solutions to fix it and explore the method to prevent the errors from creating chaos in future. So, simply stick with this blog and read the entire information and tricks.

Why Outlook Mailbox Size is full?

Users encounter Outlook mailbox size is full error when the account storage size is exceeded due to large emails and attachments, or you haven’t deleted unnecessary emails and data files from Outlook account. Besides, there are other reasons exists for the same –

• Deleted items and junk email folders are not automatically emptied.
• PST and other Outlook files grow large overtime and if not then inappropriate mailbox management can be the reason of this error.
• Calendar items, notes, and tasks can also take up a lot of space.
• Archiving policy hasn’t been implemented for older emails.
• In some scenarios, incorrect Outlook settings and configurations can cause the issue.
• At times, server hosting the Outlook mailbox also gets full as it also contains limited storage space.

Outlook mailbox size depends on the account type you are using –

• .com possesses 15 GB (free) / 50 GB+ (premium)
• Office 365/Exchange offers 50 GB – 100 GB of storage, depends on the subscription.

How to verify Mailbox Size in Outlook?

Before initiating any process, make sure to verify if the mailbox size is full or not using the below mentioned steps –

Step 1. Run Microsoft Outlook.

Step 2. Go to File, click Tools and tap Mailbox Cleanup.

Step 3. Check mailbox size of Outlook.

Step 4. Track how much space is occupied by which items.

As we are now aware about the mailbox size in Outlook, let us understand the best ways to fix Outlook mailbox size not reducing after deleting emails.

Top Different Ways to Resolve “Outlook Mailbox Size is Full”

One can fix “Outlook mailbox size not reducing after deleting emails” error by discarding already deleted files from Trash folder. Also, there are other ways exists to fix the issue. Few of them are mentioned below –

Empty Trash & Junk Folder

At times, users encounter the issue even after deleting everything because the deleted emails are transferred to Trash folder. And it takes 15 to 30 days to be deleted from there permanently. And the Junk folder includes spam emails that are not essential for users. So, we need to empty the trash or junk folder after deleting emails from Outlook mailbox. Follow the steps to know how to empty junk or trash emails in Outlook –

1. Go to the email message, right-click on it and tap Empty Folder.
2. Repeat the same process for Junk Email.

You can auto-delete using the following –

• In Outlook, go to File, click Options, tap Advanced, choose Outlook Start and Exit and select Empty Deleted items.

Drawbacks

• There will be a permanent deletion of emails. Users will face challenges when they try to recover deleted emails after they are removed from the folders unless backup is available.
• Necessary emails have been deleted by mistake which can be lost forever if they are located in these folders.

Make use of Mailbox Cleanup Tool

Outlook has a default tool to manage mailbox size –

1. Click File, navigate to Tools and select Mailbox Cleanup.
2. Now, use Mailbox Cleanup option from different cleanup options appearing.
3. The option helps viewing mailbox size/mailbox folder sizes. Also, you will be able to see items larger/older than a specified limit.
4. Mailbox Cleanup delivers the functionality to archive old items which are no more required. Tap AutoArchive to automatically transfer non-essential items to a separate folder. And with the help of its advanced options, one may filter the items required to archive. Also, one may Browse and choose the location where one need to save archived items.
5. Using the Empty option, one can permanently delete all the items exist in Deleted Items folder. However, before that, one can verify the deleted folders/subfolders if there are any with sizes.

Drawbacks

• Considerable manual pricking and deciding is needed.
• No in-depth clean for accounts with heavy attachments.

Archiving Older Emails Automatically

1. AutoArchive help relocating older items automatically into a local archive file which reduces the mailbox size.
2. Open Outlook, click File, select Options, then Advanced and then select AutoArchive Settings.
3. Set the duration to auto-archive and specify the location to store archived data.

Drawbacks

• Archive file is saved locally, so sync is not possible across devices.
• In case archived file is corrupted or somehow lost, then you will lose the data history entirely.

Note. Do not disable AutoArchive – It is a great space-saving feature.

Compress or Delete Email Attachments

Email Attachments take a lot of space –

1. Make use of Search and then Has Attachments to find and discard the attached emails.
2. Save attached files to PC or laptop and erase them from the email.

Drawbacks

• Erasing the attachments without any backup can result in data loss.
• Searching, saving and then deleting the attachments is a time-consuming task.

Increase the Size of Outlook Mailbox (Exchange & Microsoft 365 Users)

If you are utilizing Outlook as a part of business plan, then you are likely receiving Outlook mailbox full issue that is increasing mailbox size.

1. Contact with IT admin or upgrade subscription plan.
2. Some Office 365 enterprise plans show mailbox sizes offering limit 100 GB or auto-increasing archives.

Drawbacks

• Need paid subscription or extra payment.
• It increases the storage capacity in mailbox but not enhance the email management or behavior.

Compact Outlook Database File (.pst and .ost)

Once the items are removed –

1. Go to File, click Account Settings, and tap Data Files.
2. Select Files, navigate to Settings and choose Compact Now.

Drawbacks

• Compact process can only occur when the emails are deleted or removed.
• Compacting PST/OST files with large size can lead to integrity issues if the process gets interrupted.

The above manual approaches are challenging for non-technical users. So, make sure to backup Outlook data files before using any solution.

Epilogue

The write-up here offered different ways to resolve Outlook mailbox size not reducing after deleting emails. One can use the suitable solution and fix the error immediately. Also, at the same time, make sure to backup PST or OST files to prevent data loss. For any queries, contact MacMister Support.