Email servers were designed for sending small text content, and large attachments are often rejected due to size. To work around this:

1) go to FileMail.com

2) click on Send As Link

3) drag-and-drop your large file to this screen

4) Press Send, choose timeframe, then Send again

5) This generates a unique link that you can send to the recipient. Press Copy to Clipbard

6) Go to your Outlook and past the link in your message