One typed contract for seven email providers

Challenge

Transactional email code can become coupled to one provider SDK. Changing providers then spreads provider-specific request and response shapes through application features.

Approach

• Keep one typed send API in front of adapters for Resend, Brevo, Postmark, SendGrid, Mailgun, Amazon SES, and SMTP.
• Load provider SDKs as optional peers so an application installs only the adapter it selects.
• Keep templates, queues, retries, persistence, and business rules in the host application.
• Expose inbound webhook verification and normalization through a separate entry point, without taking ownership of routing or event processing.

What the implementation shows

• The same createMailer/send contract covers all seven documented providers.
• Provider contract docs and integration smoke workflows make adapter expectations and their coverage inspectable.
• The package is published as typedmailer for trusted server-side Node.js runtimes.