Some companies create their own newsletters whereas others advertise in newsletters created by others. Email newsletters can perform different functions. Some are used to periodically inform customers about new product offerings, sales, discounts and other promotions. Other newsletters are used to create communities among people with the same skills, professions or needs. Newsletters can be a way for a company to generate revenues.
Most newsletters distributed to online communities include some form of advertising.
Usually the first few paragraphs, or the last few paragraphs are advertisements for third party companies. You can build relationships with companies and insert links that contain affiliate codes in your newsletters. These codes help both companies track the recipients of the newsletters that click through the links and purchase something. Your referrals can earn you referral commissions. You can also sell sponsorship of your newsletter to companies that are interested in your audience.