How to Increase Maximum Attachment Size Limit in Outlook

When you add an email attachment to Outlook, you may receive the following 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.

Screenshot:

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 because of the default attachment size limit of 20 MB in Outlook for any Internet Email accounts. If you attempt to attach a single file exceeding 20 MB in size or multiple files whose total size exceeds 20 MB, you will encounter an error due to surpassing the set limit.

However, when utilizing the Outlook application from the Microsoft Office 365 suite and operating with a mailbox hosted on Office 365, the applicable size limits for Sent messages (Maximum Size in KB) and Received messages (Maximum Size in KB) are determined by the configurations in Exchange Online.

The default Sent messages maximum size is 35 MB (35,840 KB). Therefore, you would be able to attach files up to 35 MB in size for Microsoft 365 mailboxes.

Let’s explore the methods for increasing the file attachment limit in Outlook. First, we will examine an Outlook account not associated with Exchange Online or Exchange Server. Subsequently, we will proceed to configure this setting for Exchange Online.

1. Increase File Attachment Size in Outlook for Internet Email accounts [Non-Exchange Online/Exchange Server Mailbox]

When using Outlook with a user mailbox configured outside of Exchange Server or Exchange Online, the default attachment size limit of 20 MB applies. You can increase this limit on your Windows device by using the registry editor. Let’s review the steps.

  • Close the Outlook Application.
  • Press Win + R to open the Run dialog box, type regedit, and then press Enter. This action will launch the Registry Editor.
Increase File Attachment Size in Outlook for Internet Email accounts
Increase File Attachment Size in Outlook for Internet Email accounts
  • 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 configure File attachment size for all users.
Important Information
Replace <ver> with the value that corresponds to 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 2019/2016/365 – HKEY_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, using Outlook 2016, the registry key to navigate to is HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences. Within this registry key, right-click on an empty area, and then select New > DWORD (32-bit) Value.
Increase File Attachment Size in Outlook for Internet Email accounts
Increase File Attachment Size in Outlook for Internet Email accounts
  • 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.
Increase File Attachment Size in Outlook for Internet Email accounts
Increase File Attachment Size in Outlook for Internet Email accounts
  • To apply this change in the Outlook application, it is recommended to log out of the device and then log back in. That’s it! You have successfully increased the Outlook file attachment size to 50 MB. Now, you should be able to attach files up to 50 MB in size.
Important Note
Please note that by creating a registry entry of MaximumAttachmentSize in the HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences registry key, you have made the change specifically for the current signed-in user.

If you want to apply this change to any user who signs on to this device, create the MaximumAttachmentSize DWORD entry in the HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Preferences location.

2. Increase File Attachment Size in Outlook [Exchange Online/ Office 365/Exchange Server]

If you are using Exchange Server, Exchange Online, or Office 365 user accounts in Outlook, which is common for many organizations nowadays, you can configure the maximum email size limit in Office 365/Exchange Online.

There is no need to create the MaximumAttachmentSize registry entry. For the Exchange On-Premise server, you can configure this setting in Transport Settings through the Exchange Management Console. In the case of Exchange Online, the configuration is done using the Exchange Admin Center.

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

To increase the file attachment size in Outlook for Office 365, you can adjust the Max Send limit from the Exchange Admin Center. Alternatively, you can use PowerShell for this configuration. I’ve detailed both methods with examples in the blog post “How To Configure Max Email Size Limit In Office 365“. Follow the provided instructions to make this adjustment.

4. Increase File Attachment Size in Outlook for On-Prem Exchange Server

  • Open Exchange Management Console.
  • Navigate to Organization Configuration > Hub Transport.
  • On the Global Settings tab, choose Transport Settings.
  • In Transport Settings, go to Actions > Properties.
  • Within the Transport Settings Properties dialog box, locate the General tab.
  • Configure the value for Maximum send size (KB).

Conclusion

In this blog post, we explored various methods to increase the file attachment size in Outlook across different versions. Specifically, for Microsoft 365/Office 365 user mailboxes, you have the option to configure the maximum send file attachment size directly in Exchange Online. This can be done either for all users collectively or on an individual basis.

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