I take some issue with the comparison as an either-or.

Automation in its correct place shouldn't replace human effort - it should augment that effort.

In this case, it seems one step removed to just do both of these approaches, starting with the first. During the process of finding those 100 high-confidence matches, you could identify the ones that have the most general cases, and reuse the email copy from those.

I think the idea that automation is intended to replace human effort wholesale is improper. We should rely on automation to handle where computers are better than humans, to give the human more time to do things humans are better at.