The steps to modify the default attachment limit depend on the type of email account that you are using with Outlook.

Important This article contains information about how to modify the registry. Make sure that you back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:

322756 How to back up and restore the registry in Windows XP and Windows Vista

Internet email account (POP3, IMAP, HTTP)

To modify the default attachment limit size in Outlook for an Internet email account yourself, follow these steps: 

1. Exit Outlook.
2. Start Registry Editor.
3. Locate and then select one of the following registry subkeys:
    
   HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\Preferences
   HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\x.0\Outlook\Preferences
   Notes
   • The x.0 placeholder represents your version of Office (16.0 = Office 2016, Office 365 and Office 2019, 15.0 = Office 2013).
   • Manually create the path in the registry if it does not currently exist.
4. Add the following registry data under this subkey:
    
   Value type: DWORD
   Value name: MaximumAttachmentSize
   Value data: An integer that specifies the total maximum allowable attachment size. For example, specify 30720 (Decimal) to configure a 30-MB limit.
   Notes
   • Specify a value of zero (0) if you want to configure no limit for attachments.
   • Specify a value that is less than 20 MB if you want to configure a limit that is less than the default 20 MB.
5. Exit Registry Editor
6. Start Outlook.

Microsoft Exchange Server email account

If you are using an Exchange Server account, the 20-MB attachment limit for Internet email accounts is not used by Outlook. Instead, Outlook uses the limit that is configured on your Exchange server. To modify the setting that is used to control the size of a message that is sent through an Exchange Server account, follow these steps.

Notes

• These steps apply to Exchange Server 2007. Similar steps should be used for other versions of Exchange.
• This Exchange Server setting applies to all versions of Outlook.
  
  Note Outlook 2016 is not supported when connected to Exchange Server 2007. For more information, see KB3093039 .
• You must be an Exchange administrator to make the changes in the following steps. Regular users do not have access to the Exchange Management Console.

1. Start the Exchange Management Console.
2. Under Organization Configuration, click Hub Transport. (The screenshot for step 2 and 3 is listed below)
3. On the Global Settings tab, click Transport Settings.
   
   
4. In the Transport Settings section of the Actions pane, click Properties.
5. On the General tab in the Transport Settings Properties dialog box, configure the value for Maximum send size (KB).
6. Click OK.

Note Because the Exchange server has a cache for various settings, this change does not take effect immediately. You may have to wait several hours before this change is recognized by Outlook.