How to Increase maximum attachment size limit in Outlook

When you add an email attachment to Outlook, you may receive below error message. The error message will pop-up in Outlook Clients 2013 or later including Outlook 365 from Microsoft Office 365.

The file you’re attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead.


The file you're attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead.

You receive this error becuase of the default attachment size limit of 20 MB in Outlook for any Internet Email accounts. You could attach one file having more than 20 MB in size or multiple files where total size of all the files is more than 20 MB, you will get an error if you go over the limit.

But when you are using Outlook application from Microsoft Office 365 suite of applications and using a mailbox which is hosted on Office 365, then the Sent messages maximum size(KB) and Received messages maximum size(KB) limits apply which are configured from Exchange Online. The default Sent messages maximum size is 35 MB (35840 KB).

Therefore, you would be able to attach files upto 35 MB in size for Microsoft 365 mailboxes.

Let’s check the ways in which you can Increase file attachment limit in Outlook. First we will look into an Outlook account which is not on Exchange Online or Exchange server. Then we will configure this setting for Exchange Online.

Increase File attachment size in Outlook [Internet email accounts]

When you are using Outlook where you have configured a user mailbox which does not exist on Exchange Server or Exchange Online. In that case, 20 MB default attachment size limit will apply. You can Increase the limit on your Windows device by using registry editor. Let’s check the steps:

  • Close Outlook Application.
  • Press Win + R to open a Run box and type regedit in the Run box. Then press Enter. This will open Registry Editor.
  • Locate the following registry keys:
    • HKEY_CURRENT_USER\Software\Microsoft\Office\<ver>\Outlook\Preferences – This registry key will be used to configure File attachment size for the current user.
    • HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\ <ver>\Outlook\Preferences – This registry key will be used to configured File attachment size for all users.
Replace <ver> with the value which corresponds with the Version of Office installed on your device. For Example:

Outlook 2016/2019/365 – 16.0
Outlook 2013 – 15.0
Outlook 2010 – 14.0

– Now Registry Path for different versions of Outlook will be:
Outlook 2019/2016/365HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences
Outlook 2013 – HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Preferences
Outlook 2010 – HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences
  • In my case, I am using Outlook 2016, therefore the registry key I would be browsing to is HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences. Now, In this registry key, right-click on empty area and click on New > DWORD (32-bit) Value.
MaximumAttachmentSize create
  • Create a registry Entry MaximumAttachmentSize of Value type DWORD and provide its value in KB.
    • Value type: DWORD (32-bit) Value
    • Value name: MaximumAttachmentSize
    • Value data: An integer that specifies the total maximum allowable attachment size. For example, specify 51200 (Decimal) to configure a 50-MB limit.
  • To make this change affect in the Outlook Application. Its recommended if you LogOut of the device and Log back In. Thats It! we have increased the Outlook File attachment size to 50 MB. Now you should be able to attach files up to 50 MB in size.
Please note that by creating registry entry of MaximumAttachmentSize in HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences registry key you have only made the change for the current Signed-In user.

If you would like to apply this change to any user who will sign-on to this device then create MaximumAttachmentSize DWORD Entry in HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Preferences location.

Increase File attachment size in Outlook [Exchange Online / Office 365 / Exchange Server]

If you are using Exchange Server, Exchange Online / Office 365 user accounts in Outlook which most of the Organizations are using now a days. Then you can configure max email size limit in Office 365 / Exchange Online. You do not need to create MaximumAttachmentSize registry entry as we did in the previous section of this blog post.

For Exchange On-Prem server, this configuration can be done in Transport Settings from Exchange management console. For Exchange Online, its configured using Exchange admin center.

Increase File attachment size in Outlook for Office 365 / Exchange Online

To Increase File attachment size in Outlook for Office 365, you will need to configure Max Send limit from Exchange admin center. You can also use Powershell if you prefer. I have provided both the ways with examples on how you can perform this change. Please follow the blog post How To Configure Max Email Size Limit In Office 365 to configure it.

Increase File attachment size in Outlook for On-Prem Exchange Server

  • Open Exchange Management Console
  • Go to Organization Configuration > Hub Transport.
  • On the Global Settings tab, select Transport Settings.
  • In the Transport Settings > Actions > Properties.
  • General tab in the Transport Settings Properties dialog box, configure the value for Maximum send size (KB).


In this blog post, we have seen different ways we can increase the File attachment size in Outlook for various Outlook versions. If you are using Microsoft 365 / Office 365 users mailboxes then you can configure Max Send file attachment size directly in exchange online for all users at once or just for one user.

Leave a Comment