These are the steps:

  • Click "Attach File" button which should look like a paperclip.
           
  • Click "Browse" to search for the file.
  • Find the file you want to attach and click it. This should highlight the file. 
  • Click the Open button. This puts the filename and location in the box, next to the "Browse" button. If you need to attach multiple files click "Choose more files".
  • Click "Attach" button on the bottom.
  • Send your message as usual.

The maximum size of an attachment that you can send depends on the email client you use. The limits for attachments are the following:

  • Outlook Web App is limited to 25MB.
  • Outlook for Mac is limited to 35MB.
  • Outlook is limited to 150MB.
The limits of the entire email size including attachments are the following:
  • Outlook Web App is limited to 112MB.
  • Outlook for Mac is limited to 35MB.
  • Outlook is limited to 150MB.