Hi Andrew:
This appears to be a few possible ideas.

1. An invoice spec that looks like a letter - would this mean that we would have to reprint the so-called Invoices, say at day-end (or the next day), using the letter-spec?

2. The second idea looks more intensive. We would have to export the data to Excel, and then go into Word, do the mailmerge and then send all the letters to email. (How would Word know which letter goes to which email?)

If this is what you are recommending, I like the first option. There is less fidgeting about for the end-user.