You might want to look at Sage Alerts and Work Flow.

Path of least resistance: Consider smaller batches or breaking bigger batches into smaller chunks by using the selection grid to filter what is being processed by invoice # range.

Rather than batching, would it help you to send invoices electronically at time of shipment or invoice creation?
We used to batch our invoices next day. Now we send immediately at time of shipment. It eliminated a few steps in our process and saved time overall. Customers love it as they get to see their order processed in real time.

We import 4000+ invoices into an AR invoice batch every month, more than 1000 of these are emailed and that number is growing steadily as we move to paperless.
We use batches - that's not going to change.

Currently we're fumbling through the process, it takes about 6 hours to email these invoices. There are errors encountered and the email process stops and waits for a user to click something - not really efficient. Then we have to figure out which invoices were not emailed and resend them, ugh what a waste of time and resources.

Sure we can break the batch up into multiple batches, but at the end of the day we still need to get 1000+ emails out.
There has to be a better way.

I looked at Sage Alerts - its not going to be fun to rewrite the invoice report.

Print to PDF, then use a 3rd party tool to query the PDF log then attach those files to emails.

Here is a tip on the Sage Alerts. Using an Access database as a data source create SQL pass through queries reading the Invoice Data Entry tables. Create another query that is the same name as the works table and has the same fields. Then change the data source of the report to the Access database.

Brilliant! So simple and elegant.