How to increase the attachment size limit in Outlook?

Link the maximum size of Outlook to the maximum size of your mail server

By default, Outlook does not send email messages with attachments larger than 20 MB, but many mail servers allow attachments of 25 MB or more. If your mail server allows larger attachments, ask Outlook to send messages larger than 20 MB. You can also avoid receiving undelivered messages if the default Outlook exceeds what you can send through your email server.

The instructions in this article apply to Outlook 2019, Outlook 2016, Outlook 2013, Outlook 2010, and Outlook for Office 365.

How to increase the attachment size limit in Outlook?

When you send an email attachment in Outlook, you may receive an error message warning that the attachment exceeds the size limit. If your mail server allows messages up to 25 MB and the file attachment is slightly larger than the default limit of 20 MB, change the Outlook default value to match the default size of the mail server.

Before making any changes to the Windows Registry, back up the registry so that you can restore your system to its original state if you make changes.

  1. Click Windows+R

  2. In the dialog box Run enter regedit

  3. Select Okay

  4. Navigate through the registry tree and navigate to the entry that corresponds to your version of Outlook:

    • Outlook 2019 and 2016 : HKEY_CURRENT_USERSoftwareMicrosoftOffice16.0Outlook\Settings
    • Outlook 2013 : HKEY_CURRENT_USER SoftwareMicrosoftOffice15.0Outlook\Settings
    • Outlook 2010 : HKEY_CURRENT_USER SoftwareMicrosoftOffice14.0Outlook\Settings

  5. Double tap the value Maximum attachment size

    If you don’t see MaximumAttachmentSize, add the registry key and value. Go to Change select New DWORD value enter Maximum attachment size and press Enter

  6. In a text box Data value Enter the desired attachment size limit in KB. For example, to set the maximum size to 25 MB, type 25600

    • The default value (when MaximumAttachmentSize is missing) is 20 MB or 20480.

    • To limit the file size of attachments, type 0 † Most mail servers have a size limit, so 0 is not recommended; You may get large messages back as undeliverable.

    • The limit corresponds to the limit of your mail server. Lower the Outlook limit by 500 KB to free up some leeway.

  7. Select Okay

  8. close to registry editor

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