offering some free advice

Free advice is always welcome. And given the giver, it will be taken very seriously...

Your suggestion seems the most sensible. There are occasions when we get upwards of 100 new registrations in a day but those are very rare days. So the volume of data could easily be manually verified. The only issue being an automated email immediately after registration in many cases. Perhaps I need to anonymise that one.

It's actually more complex still because we hold people's pets' names in our database and send some emails as Dear Eyespop and Fido. Plus, we add the dog's name into the body content. But it has to make sense when the name is present and when it is missing.