MailChimp is an online email marketing service that helps businesses reach customers and prospects. It offers automated marketing campaigns and provides customers with detailed analytics of the results. MailJet is very similar in that it is also an email marketing service, but it is designed for businesses that need to send large volumes of emails. MailJet provides more tools and analytics for businesses to monitor their campaigns, and offers the ability to create tailored messages for targeted audiences. MailJet also has more advanced features such as automatically optimizing content, A/B testing of email messages and automated segmentation. In summary, MailChimp and MailJet offer similar services, but MailJet provides more features and analytics to optimize email campaigns and target specific audiences.