Mailrelay and SendGrid are both popular email marketing platforms that offer a range of features to help businesses manage their email campaigns. One of the main differences between the two platforms is their pricing structure. Mailrelay offers a free plan with limited features, while its paid plans are more affordable than SendGrid's plans. On the other hand, SendGrid offers more robust features and integrations, making it a better choice for businesses with more complex email marketing needs. Additionally, while both platforms offer email automation, SendGrid's automation capabilities are more advanced than Mailrelay. Ultimately, the choice between the two platforms will depend on the specific needs and budget of the business.