Which of these is a good practice to keep in mind when sending emails to your contacts?

Which of these is a good practice to keep in mind when sending emails to your contacts?

• Run an A/B test on your subject line to determine which one works best
• Send the same generic and simple message to your entire contact database
• Include enough content in the email so there is no need for them to click away to read further elsewhere
• Only include a call-to-action on the landing page you’re linking to in the email