Finding the best time of day, email subject line, content or call-to-action can be a trial and error. For best results when A/B testing we recommend you alter one element at a time, multiple tweaks to your email in one test will not help you to figure out which element people respond to best. This type of research can take some time, but there is no substitute to getting to know your client. Their likes, dislikes, and buying habits can prove to be invaluable for future marketing campaigns.