The author of the open-source project EmailEngine shares their experience of turning it into a full-time business. Initially, the project was released under an AGPL license with an option to subscribe for an MIT-licensed version, but this model did not generate significant revenue. The author then changed the license to commercial and implemented a license key system, which led to a substantial increase in revenue. This change allowed the author to work on the project full-time and earn a decent income.