Safelists are an opt-in email service that allows you to send your ad to their list at intervals of anywhere from once a day to once a week. In return for this service, you are expected to read other members ads. Most are free to join. You may also pay a small fee allowing you to post both more often and to more people.
Open yourself a separate email account and keep it clean, if you bounce emails from the Safelists you will be banned from using them. Recommended is Gmail.com
Be creative with your headlines. A unique headline for your advertisement will help attract attention to your ads, making them stand out from the mass of ads that people will be receiving.
You need to be aware that most safelists are populated by internet marketers, who are more interested in marketing their own products, than in reading your advertisement.
But, there will be people who will read your ads and who will respond - just don't expect to make thousands of dollars of income from them.
We Highly Recommend that you read - The Safelist Tactics Guide here.