Shared Email Templates
Attach files to Outlook emails with the Message attachments button
With the Message attachments button on the template editor toolbar, you can attach files from OneDrive, SharePoint, and URLs.
When creating or editing an Outlook email template, select the
Message attachments button on the template editor toolbar.Choose where your file will come from (OneDrive, SharePoint, or a URL) and click the plus sign next to the corresponding option.
Select a file or enter a URL.
Close the Message attachments dialog.
A blue dot will appear on the Message attachments button:

Save the template.
When you use the template, the specified attachments will be automatically added to your email.