Once you ship the order you are likely updating an invoice - which is essentially a copy of the sales order. Use paperless office to enable electronic delivery for this customer and during the invoice posting process, an invoice can be emailed to them.

We do not invoice the sales order once shipped.  Sometimes the SO is not invoiced for days or weeks after the SO has shipped, multiple reasons.

Sage Alerts and Work Flow can do this.  It would monitor the sales order invoice data entry files and when an invoice for this customer is created it would run a crystal report that would create the sales order or packing list or invoice, really anything you want, and email it to the customer.

The issue I'd be concerned with is potential back-order quantities... which is why creating the invoice (unposted) and emailing that (using Paperless) is probably a better idea, to ensure accurate numbers.

If 100% of shipments are full (and there are never, never, never any shipments of anything less than the full order), then an automated report based on a checkbox (to indicate when the SO shipped) could work.