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How to Increase the Outlook Attachment Size Limit


Business man sitting in stairwell using computer
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The attachment size exceeds the allowable limit.


Outlook's refusal to send would be okay if you'd share a 200 MB video; but a few puny images, a tenth that size and few MB maybe — when you know your mail server will let you send messages up to 25 MB?

By default, Outlook will not send messages whose attachments exceed 20 MB. Fortunately, you can tell it about your mail server's allotment, to send messages larger than the default if your server allows it, or to avoid getting back undeliverable messages if Outlook's default is larger than what you can actually send.

Increase the Outlook Attachment Size Limit

To change the size Outlook will allow as a maximum for attachments to send:

  • Type "regedit" in in the Start menu's Start Search field.
  • Select regedit under Programs.
    • Under Windows XP, select Run… from the Start menu and type "regedit" followed by Enter.
  • Travel down the registry tree to HKEY_CURRENT_USER\­Software\­Microsoft\­Office\­14.0\­Outlook\­\Preferences.
  • Double-click the MaximumAttachmentSize value.
    • If you cannot see MaximumAttachmentSize:
    • Select Edit | New | DWORD Value from the menu.
    • Enter "MaximumAttachmentSize" (not including the quotation marks).
    • Press Enter.
    • Now double-click the MaximumAttachmentSize value you just created.
  • Enter the desired attachment size limit in KB under Value Data:.
    • To set a size limit of 25 MB, for example, use "25600".
    • The default value (with MaximumAttachmentSize not present) is 20 MB or "20480".
    • For no attachment file size limit, enter "0". Practically all mail servers do have a size limit, though, so "0" is not recommended; you would invariably get large messages back as undeliverable after an often long and fruitless uploading process.
    • Ideally, the limit corresponds to your mail server's limit. You can reduce the limit by some 500 KB to allow wiggle room.
  • Click OK.

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