Click "Generate New Link," and then grab that link. Then you can link it to your Twitter sharing button. Or, if you're segmenting your list by attributes such as "has Twitter" or "topic of recent conversion: social media" (you'll need marketing intelligence software like HubSpot for this), you can even include it in your main email copy, like this:
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.