A/B Testing is an experiment comparing two versions of a message, page, ad, or element to see which performs better.
It matters because email is one of the few channels a business can own directly. Strong email fundamentals improve trust, deliverability, segmentation, and long-term lead nurturing.
Example
A team randomly divides an eligible audience between two versions of one call to action. It chooses the success measure before sending and waits for sufficient comparable observations instead of declaring a winner from the first few clicks.