Personalize your email subject line based on user info. Experian, MailerMailer and Mailchimp have done studies showing that personalised a subject lines results in a 22.3 percent increase in open rate over emails without personalization. Many companies choose not to collect any personal data with email addresses to keep their sign up forms as frictionless as possible. If you want to send emails with personalized subject lines while keeping your sign up forms simple, you should at least collect first names with email addresses.