SendGrid offers a robust solution for developers to send customized transactional emails via websites or mobile applications, using HTML and CSS styled templates created in the SendGrid Admin Portal. The process involves creating a dynamic transactional template, which can be triggered through a simple API call, and integrating it with PubNub to automate email delivery. Developers can set up a free account on SendGrid to create a template, customize it with variable substitutions, and test its functionality. By integrating PubNub, developers can send a publish message containing user details, which is processed by a serverless function and formatted into an XHR POST to be sent by SendGrid. The setup requires importing the PubNub JavaScript SDK, deploying the SendGrid block, and storing API keys in a function vault for secure access. Once configured, this setup allows automated emails to be sent whenever a PubNub publish message is sent, facilitating seamless communication with users.