I've mentioned this add-on in the past (years ago) as I still think it is a vital addition that should be added asap.
When someone makes an online purchase they should receive a tracking number and link to the postal companies tracking site.

This could easily be an add-on via a pop-up page after pressing an image next to the 'mail to' or 'pdf' icon to add just 2 lines to be sent with the confirmation email 'order confirmed' or added to the invoice.

Such as -
Tracking Number (default text = not available)
Website address for tracking (default text = last input or set).

For me, this would complete the package and make things a lot easier for my online ordering side.

Thanks.

That should be 'sent' not 'confirmed' status for adding tracking number to the email confirmation.