Mailrelay is an email marketing tool that provides a complete solution for effective email marketing campaigns. It has a wide range of features and tools which help marketers build and automate their email campaigns. It includes an automatic contact segmentation system, advanced analytics, customized templates, high-end deliverability, and a powerful API.
MailerLite is an email marketing tool specifically tailored for small businesses and startups. More lightweight than Mailrelay, it offers easy-to-use email marketing tools such as customizable templates, CRM integration, A/B testing, and much more. It also provides analytics to gauge your campaigns success, but does not offer as many API-based options as Mailrelay.