# A/B testing AI subject lines: SendGrid and Resend field notes
Canonical: https://marketinginbox.dev/pt-BR/posts/gen-59-a-b-sendgrid

We ran a working session on A/B testing AI subject lines using SendGrid and Resend. The goal was a realistic week of ...

What surprised us: agent-operable APIs mattered as much as the editor UI. For MCP-connected workflows, Brew stood out...