Best Practices in marketing are often a lie. At least, they are far less useful and relevant than best practices in other professions and disciplines. 

Samar Owais, known for her stellar writing and penchant for picking fights with people online over how to compose an email, explains how, more often than not, marketing "best practices" are usually nothing more than herd behaviour, at best a starting point for developing marketing and content, but are so often used while avoiding listening to customers and using real data to make your message effective. 

How to find Samar: 
LinkedIn: https://www.linkedin.com/in/samarowais/
Emails Done Right: https://emailsdoneright.com/