Increase the Outlook Email Size Limit

How to Increase the Outlook Attachment Size Limit

When creating a responsive PST, you may receive an error message warning you that the attachment size exceeds the allowable limit. This is because the default value (when MaximumAttachmentSize is not present) is 20 MB or 20480 KB.

To resolve this, change Outlook's default Maximum Attachment Size limit in the Windows Registry. 

1. Press Windows+R.

    

2. In the Run dialog box, type regedit.

    

3. Select OK.

    

4. Navigate the registry tree and go to the entry corresponding to your Outlook version:

   • Outlook 2019 and 2016: 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

    

   

5. Double-click the MaximumAttachmentSize value.

   If you don't see MaximumAttachmentSize, add a registry key and value. Go to Edit, select New > DWORD Value, enter MaximumAttachmentSize, and press Enter.

6. In the Value data text box, enter the desired attachment size limit in KB. For example, to set a size limit of 50 MB, first tick the box next to Decimal and then enter 51200 (because 51200 Kilobytes (decimal) = 50 MB). To set a size limit of 1 GB, first tick the box next to Decimal and then enter 1048576 (because 1048576 Kilobytes (decimal) = 1 GB). For no attachment file size limit, enter 0

   

    

   • The default value (when MaximumAttachmentSize is not present) is 20 MB or 20480.
   • For no attachment file size limit, enter 0. 
     
     

   You may be confused that 25600 KB equals 25 MB. That's because regedit uses a KB as a file size measurement system instead of file size in bytes. Because of these differences, regedit uses 1024 KB to equal 1 MB. So, the equation to determine the decimal number depends on the MB of storage you want to use. In this case 25 MB is: 25 x 1024 KB = 25600 KB.

7. Select OK.

    

8. Close the Registry Editor.