If you're using Outlook or some other similar platform to send out bulk emails, you could get yourself into a lot of hot water.
Here's a classic example of an email marketing faux pas that arrived in my inbox last week from a local beautician.
How to irritate your customers by showing their personal emails to all your other customers
To: List of the personal email addresses of 160 clients all showing to every recipient.
Offer containing several typos
I was not terribly impressed but these things happen. And I had this vision of a receptionist at the business looking at the computer with horror at what had just happened.
The following day, I received a second message from them
To: List of the personal email addresses of 160 clients - again listing the personal email addresses of their entire database