Use REST for your application and MCP for the agent helping you. Your production code shouldn't send password resets through an AI model, and your coding agent shouldn't need you to paste curl commands. They solve different problems, and most teams will use both.
What each one is for
A REST API is called by code you wrote. The request is the same every time, so it's predictable, fast, and easy to test. That's what you want for an OTP or a receipt, where a decision has already been made and only the sending is left.
MCP (Model Context Protocol) is how an AI agent discovers and calls tools. The agent reads what tools are available and decides which to use, based on what you asked. That suits work that varies: setting up a domain, finding out why a customer didn't get an email, or writing the integration in the first place.
A simple way to choose
- A customer action triggers the email: REST.
- You'd otherwise do it by hand in a dashboard: MCP.
- An agent is your product, and it decides when to email: MCP or REST both work. MCP is quicker to connect, and REST gives you more control over what the model can do.
Why you shouldn't route production mail through an agent
Every call through a model adds time and cost, and the model might decide differently from one run to the next. For mail your business depends on, that variation has no upside. A password reset should go out the same way every time.
Credentials are the other reason. Give your application a key limited to what it needs, and give an agent its own connection, so you can remove one without touching the other. On MailKaka, a key used through MCP also has its own daily cap, separate from the REST traffic on that key.
Using both on MailKaka
Connect your agent over MCPto set things up, then send from your application with theREST API. Both use the same domains, logs, suppression list, and plan quota, so your agent can check on email your application sent.