Use Mobile Locker in Classic Outlook

From your inbox, click New Email.

The Mobile Locker button should appear on the ribbon. 

When the Mobile Locker sidebar opens, you can click Get Started and follow the instructions to sign in if this is the first time you open the plugin.

Select Global as the region and input your email address and password. Click Continue.

Once signed in, you will see the Library tab and the list of folders.

Start writing your email and ensure the cursor is where you want the links to go.

Navigate to the folder and find the file(s) you want to share. Click the checkbox below each one, then click Insert # links at the bottom of the plugin.

The links will appear in the email where your cursor was positioned. Continue writing the email and then click Send.