What legal issues are there with triggered email?
First off, I'm not a lawyer and you should consult a lawyer to get an answer specific to your business.
But I can point you to some resources that I've found related to legal issues surrounding this type of marketing email.
The main things that you need to take care of when sending marketing email of any kind are:
- Having an opt-out link in the footer - Including your physical address in the footer - An opt-in or prior business relationship - You're not selling their information to a 3rd party
Europe's laws are a bit more strict than the United States - but in both cases, an existing business relationship constitutes (the customer coming to your site and entering their information / placing an order) an opt-in.
Here's a good resource for additional information.
Also, for what it's worth, I've had a few German customers tell me that they weren't able to send this type of marketing email. However I also have one German customer that has said it's okay and is sending them.