Mailing lists are often rented or sold. If rented, the renter agrees to use the mailing list for only contractually agreed-upon times. The mailing list owner typically enforces this by "salting" (known as "seeding" in direct mail) the mailing list with fake addresses and creating new salts for each time the list is rented. Unscrupulous renters may attempt to bypass salts by renting several lists and merging them to find the common, valid addresses.
Address subscribers by name. Personalized emails are more successful. Buffer also suggests to personalize your emails based on need by sending emails that meet different user expectations. This makes them more targeted and more likely to be successful. Some studies show that educating and segmenting your audience will boost your click through rate on emails by up to 50%.