You split your email subscriber list into “cold” vs. “warm” leads so you can compare similar groups of customers in this test. You prepare two versions of your email—one with the normal subject line, and one with a much shorter, punchier subject line. You send half of your cold leads the normal subject line and half of your cold leads get the new, exciting subject line. You also send half of your warm leads the normal subject line, and the other half get the new subject line.
Amazing list of free solo ad websites. I have never believed in solo-ads. But I will definitely try them and see. As you said copy-writing , landing page, split-testing skills will help us a lot in getting good conversions . Really great tip on creating new email accounts to get free credits. Tracking your clicks and visitors will let you know that if we are getting good conversions.

Open and click-through rates (CTRs): Knowing who are engaged customers (those who open most emails and end up making purchases) versus inactive customers (who haven’t opened any emails in months) can be invaluable. Marketing campaigns announcing a new product should absolutely include those engaged customers, while re-engagement campaigns can be created to try and entice the inactive customers.
Sometimes low-hanging fruit is as easy as it looks. Personalizing emails, as well as segmenting them—a marketing technique that teases out your subscriber list to send relevant emails to specific subscribers—can offer significant returns. Segmenting emails allows you to target specific groups of subscribers, which leads to substantial increases in click-through rate.
When it comes to deciding how to craft that perfect subject line, there appears to be really only one area to avoid: the subject line of 60 to 70 characters. Marketers refer to this as the “dead zone” of subject length. According to research by Adestra, which tracked over 900 million emails for its report, there is no increase in either open rate or clickthroughs at this 60-to-70 character length of subject line.