The subject is one of the most important components of your E-Mail campaign. The more meaningful your subject is, the more successful your E-Mail-campaign will be.
You can also personalize the subject. For that you can use the address fields of your address database (first name, last name, country, e.g.) in the subject to address your recipient more personal.
For that klick the button "add field" and choose a fitting address field from your database.