How to Increase the Attachment Limit in Classic Outlook

Classic Outlook may block a large attachment before you can send it. You can raise its local attachment limit for a POP or IMAP account through the Windows registry, but the mail provider and recipient can still reject an oversized message. If either side has a lower limit, send a OneDrive link instead.

Before changing the limit

Check the size of all attachments together, not just the largest file. The steps below apply to classic Outlook for Windows. They do not raise limits in new Outlook, Outlook.com, or an Exchange or Microsoft 365 mail server. If you use a work or school account, ask your administrator about the server limit before changing your PC.

Increase the classic Outlook limit for a POP or IMAP account

1. Close Outlook. Back up the registry before making changes: open Registry Editor (regedit), select the relevant key, and use File > Export.
2. In Registry Editor, go to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences. Use 15.0 in place of 16.0 for Outlook 2013; 16.0 covers classic Outlook 2016, 2019, 2021 and Microsoft 365.
3. Right-click an empty area in the right pane and choose New > DWORD (32-bit) Value. Name it MaximumAttachmentSize. If it already exists, open it.
4. Select Decimal, then enter a size in kilobytes. For example, 30720 sets a 30 MB client limit. Select OK and restart Outlook.

This setting changes Outlook's local check only. It cannot override your email provider's limit, an Exchange policy, or the recipient's limit. A message can also grow in transit because of attachment encoding, so leave room below the service's stated maximum. If sending still fails, use a smaller file or a share link. Microsoft's Outlook attachment limit guidance documents the registry setting.

Send a larger file with a link

In an Outlook message, attach the file and, if Outlook offers it, choose the option to upload and share it through OneDrive instead of sending a copy. You can also upload it to OneDrive first, select Share, review who can open the link and whether they can edit, then paste the link into your email. See how to protect OneDrive sharing links when access should be limited.

For a file that may shrink enough, create a ZIP archive and check its size before attaching it; already compressed photos and video often shrink little. Follow the Windows 11 ZIP instructions if you need that option.