Microsoft 365 atWork partners with AFI.AI, the developer of modern data protection platform built from the ground up to deliver a fully-fidelity backup for MICROSOFT 365 and GOOGLE WORKSPACE.


If you are using a heavily Outlook mailbox you can get to the point where your Outlook mailbox is full and you can't send messages.

Learn how to resolve the "Outlook Mailbox Is Full Can’t Send Messages" Error.

If you are getting more and more emails to your Outlook account you can get to the point when your Outlook mailbox will be full. Exchange Online offers great functionalities around professional email service but limits the size of the email box to a maximum of 50/100 GB size. Moreover, your IT could limit the maximal size of your mailbox to a smaller size like 1GB.

If you will receive a huge number of emails or big attachments your Outlook could become full.

Learn how to resolve Outlook Mailbox is full error.


What is the size of my Outlook mailbox?

You can check the size of your mailbox in the Outlook application.

To determine your mailbox size open Outlook for to Folder (1), Folder Properties (2) and Folder Size (3). In the new screen you will find exacts numbers that describes size of your mailbox.


Remember that 1 GB is 1,000,000 KB. You will need to do the calculation to convert the size of the mailbox to a more friendly format 😉


Another way to check the size of your mailbox is to check Mailbox Settings in your Outlook application. In the Outlook app go to the File tab.

In the File tab, you will be able to fin Mailbox Setting and find the size of your mailbox in a more friendly format.


"Outlook Mailbox Is Full Can’t Send Messages" error

If the size of your mailbox reaches the limit set in Office 365 you will not be able to send and receive new messages. Your Outlook application will display "Outlook Mailbox is Full" error message with the information "there is not enough memory available to perform the operation".

You need to reduce the size of your mailbox by doing the clean-up operation.



How to reduce the size of Outlook mailbox

If your Outlook mailbox is full and you cannot send and receive new messages you will need to reduce the size of your mailbox. You need to start the do the cleanup of your mailbox. I will present you with a few tricks that will help you to reduce the size of your mailbox.

1. Do the cleanup of your Outlook mailbox

The first way available in the mailbox setting is the option Mailbox Cleanup (1). In this section you will have a few available option that will help to do the cleanup.

  • Finding the old items and large items in Find (1)
  • Setting up of AutoArchive (2) - setting up the rul that will Archive old emails
  • Empty (3) Deleted emails
  • Clean up (4) the alternate versions of the same emails in the mailbox

All these activities could help you free some space in your mailbox.


2. Empty deleted items folder

Remove all emails stored in Deleted Items Folder (2) and clean up deleted emails.

You will regain the space taken by deleted emails.


3. Archive old emails

One of the most valuable solutions that could clean up the mailbox is archiving the emails to dedicated PST file stored locally. This kind of emails will be moved out from your mailbox to a locally stored PST file.

In the setup of Archiving, you will be able to decide the date that will be the border for the archiving process.

I would like to recommend you store this PST file in your local OneDrive folder - it will deliver the backup solution for your emails. You will not have to worry about possible local drive corruption.

This could be one of the most effective ways to shrink the size of your email box.


4. Move your email attachments from Outlook to OneDrive

You can create a Power Automate rule that will backup/move all attachments from Outlook to your OneDrive account. Use the available Power Automate template and move the attachments to OneDrive.


How to do not lose Outlook mailbox data

You did learn how to do the cleanup of your Outlook mailbox when it is full. Remember that during massive deletion of your emails you can remove one or two important ones.

Before you will start the cleanup process consider to:

  1. Make a copy of your mailbox pst file.
  2. Make a copy of any Archives attached to your mailbox.
  3. Do the backup of your Outlook mailbox.

These options will allow you to restore in Outlook important emails that could be deleted from your full mailbox. A complex email backup solution will give you the additional possibilities to search and restore a single email. Use a free trial of the Email backup platform to give yourself a chance to restore deleted emails.



Learn how to resolve Outlook Mailbox Is Full Can’t Send Messages error and clean up fix your Outlook mailbox. Clean up your Outlook mailbox and reduce its size.