const response = await fetch('https://api.resend.com/emails', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${env.RESEND_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    from: 'noreply@yourdomain.com',
    to: 'user@example.com',
    subject: 'Welcome!',
    html: '<h1>Hello World</h1>',
  }),
});

const data = await response.json();
// { id: "49a3999c-0ce1-4ea6-ab68-afcd6dc2e794" }

const response = await fetch('https://api.sendgrid.com/v3/mail/send', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${env.SENDGRID_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    personalizations: [{
      to: [{ email: 'user@example.com' }],
    }],
    from: { email: 'noreply@yourdomain.com' },
    subject: 'Welcome!',
    content: [{
      type: 'text/html',
      value: '<h1>Hello World</h1>',
    }],
  }),
});

// Returns 202 on success (no body)

const formData = new FormData();
formData.append('from', 'noreply@yourdomain.com');
formData.append('to', 'user@example.com');
formData.append('subject', 'Welcome!');
formData.append('html', '<h1>Hello World</h1>');

const response = await fetch(
  `https://api.mailgun.net/v3/${env.MAILGUN_DOMAIN}/messages`,
  {
    method: 'POST',
    headers: {
      'Authorization': `Basic ${btoa(`api:${env.MAILGUN_API_KEY}`)}`,
    },
    body: formData,
  }
);

const data = await response.json();
// { id: "<20111114174239.25659.5817@samples.mailgun.org>", message: "Queued. Thank you." }

const response = await fetch('https://api.smtp2go.com/v3/email/send', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    api_key: env.SMTP2GO_API_KEY,
    to: ['<user@example.com>'],
    sender: 'noreply@yourdomain.com',
    subject: 'Welcome!',
    html_body: '<h1>Hello World</h1>',
  }),
});

const data = await response.json();
// { data: { succeeded: 1, failed: 0, email_id: "..." } }

undefined

undefined

undefined

undefined

// Resend
interface ResendEmail {
  from: string;
  to: string | string[];
  subject: string;
  html?: string;
  text?: string;
  cc?: string | string[];
  bcc?: string | string[];
  replyTo?: string | string[];
  headers?: Record<string, string>;
  attachments?: Array<{
    filename: string;
    content: string; // base64
  }>;
  tags?: Record<string, string>;
  scheduledAt?: string; // ISO 8601
}

interface ResendResponse {
  id: string;
}

// SendGrid
interface SendGridEmail {
  personalizations: Array<{
    to: Array<{ email: string; name?: string }>;
    cc?: Array<{ email: string; name?: string }>;
    bcc?: Array<{ email: string; name?: string }>;
    subject?: string;
    dynamic_template_data?: Record<string, unknown>;
  }>;
  from: { email: string; name?: string };
  subject?: string;
  content?: Array<{
    type: 'text/plain' | 'text/html';
    value: string;
  }>;
  template_id?: string;
  attachments?: Array<{
    content: string; // base64
    filename: string;
    type?: string;
    disposition?: 'inline' | 'attachment';
  }>;
}

// Mailgun
interface MailgunEmail {
  from: string;
  to: string | string[];
  subject: string;
  html?: string;
  text?: string;
  cc?: string | string[];
  bcc?: string | string[];
  'h:Reply-To'?: string;
  template?: string;
  'h:X-Mailgun-Variables'?: string; // JSON
  attachment?: File | File[];
  inline?: File | File[];
  'o:tag'?: string | string[];
  'o:tracking'?: 'yes' | 'no';
  'o:tracking-clicks'?: 'yes' | 'no' | 'htmlonly';
  'o:tracking-opens'?: 'yes' | 'no';
}

interface MailgunResponse {
  id: string;
  message: string;
}

// SMTP2Go
interface SMTP2GoEmail {
  api_key: string;
  to: string[];
  sender: string;
  subject: string;
  html_body?: string;
  text_body?: string;
  custom_headers?: Array<{
    header: string;
    value: string;
  }>;
  attachments?: Array<{
    filename: string;
    fileblob: string; // base64
    mimetype?: string;
  }>;
}

interface SMTP2GoResponse {
  data: {
    succeeded: number;
    failed: number;
    failures?: string[];
    email_id?: string;
  };
}

// templates/password-reset.ts
export async function sendPasswordReset(
  provider: 'resend' | 'sendgrid' | 'mailgun' | 'smtp2go',
  to: string,
  resetToken: string,
  env: Env
): Promise<{ success: boolean; id?: string; error?: string }> {
  const resetUrl = `https://yourapp.com/reset-password?token=${resetToken}`;

  const html = `
    <h1>Reset Your Password</h1>
    <p>Click the link below to reset your password:</p>
    <a href="${resetUrl}">Reset Password</a>
    <p>This link expires in 1 hour.</p>
  `;

  switch (provider) {
    case 'resend':
      return sendViaResend(to, 'Reset Your Password', html, env);
    case 'sendgrid':
      return sendViaSendGrid(to, 'Reset Your Password', html, env);
    case 'mailgun':
      return sendViaMailgun(to, 'Reset Your Password', html, env);
    case 'smtp2go':
      return sendViaSMTP2Go(to, 'Reset Your Password', html, env);
  }
}

async function sendViaResend(
  to: string,
  subject: string,
  html: string,
  env: Env
): Promise<{ success: boolean; id?: string; error?: string }> {
  const response = await fetch('https://api.resend.com/emails', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${env.RESEND_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      from: 'noreply@yourdomain.com',
      to,
      subject,
      html,
    }),
  });

  if (!response.ok) {
    const error = await response.text();
    return { success: false, error };
  }

  const data = await response.json();
  return { success: true, id: data.id };
}

async function sendBatchResend(
  recipients: string[],
  subject: string,
  html: string,
  env: Env
): Promise<Array<{ email: string; id?: string; error?: string }>> {
  const results: Array<{ email: string; id?: string; error?: string }> = [];

  // Chunk into groups of 50
  for (let i = 0; i < recipients.length; i += 50) {
    const chunk = recipients.slice(i, i + 50);

    const response = await fetch('https://api.resend.com/emails', {
      method: 'POST',
      headers: {
        'Authorization': `Bearer ${env.RESEND_API_KEY}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        from: 'noreply@yourdomain.com',
        to: chunk,
        subject,
        html,
      }),
    });

    if (response.ok) {
      const data = await response.json();
      chunk.forEach(email => results.push({ email, id: data.id }));
    } else {
      const error = await response.text();
      chunk.forEach(email => results.push({ email, error }));
    }
  }

  return results;
}

async function sendBatchSendGrid(
  recipients: Array<{ email: string; name?: string; data?: Record<string, unknown> }>,
  templateId: string,
  env: Env
): Promise<{ success: boolean; error?: string }> {
  const response = await fetch('https://api.sendgrid.com/v3/mail/send', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${env.SENDGRID_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      personalizations: recipients.map(r => ({
        to: [{ email: r.email, name: r.name }],
        dynamic_template_data: r.data || {},
      })),
      from: { email: 'noreply@yourdomain.com' },
      template_id: templateId,
    }),
  });

  if (!response.ok) {
    const error = await response.text();
    return { success: false, error };
  }

  return { success: true };
}

npm install react-email @react-email/components

// emails/welcome.tsx
import {
  Html,
  Head,
  Body,
  Container,
  Heading,
  Text,
  Button,
} from '@react-email/components';

interface WelcomeEmailProps {
  name: string;
  confirmUrl: string;
}

export default function WelcomeEmail({ name, confirmUrl }: WelcomeEmailProps) {
  return (
    <Html>
      <Head />
      <Body style={{ fontFamily: 'Arial, sans-serif' }}>
        <Container>
          <Heading>Welcome, {name}!</Heading>
          <Text>Thanks for signing up. Please confirm your email address:</Text>
          <Button href={confirmUrl} style={{ background: '#000', color: '#fff' }}>
            Confirm Email
          </Button>
        </Container>
      </Body>
    </Html>
  );
}

import { Resend } from 'resend';
import WelcomeEmail from './emails/welcome';

const resend = new Resend(process.env.RESEND_API_KEY);

await resend.emails.send({
  from: 'noreply@yourdomain.com',
  to: 'user@example.com',
  subject: 'Welcome!',
  react: WelcomeEmail({ name: 'Alice', confirmUrl: 'https://...' }),
});

import { render } from '@react-email/render';
import WelcomeEmail from './emails/welcome';

const html = render(WelcomeEmail({ name: 'Alice', confirmUrl: 'https://...' }));

await fetch('https://api.resend.com/emails', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${env.RESEND_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    from: 'noreply@yourdomain.com',
    to: 'user@example.com',
    subject: 'Welcome!',
    html,
  }),
});

// 1. Create template in SendGrid dashboard with handlebars
// Subject: Welcome {{name}}!
// Body: <h1>Hi {{name}}</h1><p>Your code: {{confirmationCode}}</p>

// 2. Send with template ID
const response = await fetch('https://api.sendgrid.com/v3/mail/send', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${env.SENDGRID_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    personalizations: [{
      to: [{ email: 'user@example.com' }],
      dynamic_template_data: {
        name: 'Alice',
        confirmationCode: 'ABC123',
      },
    }],
    from: { email: 'noreply@yourdomain.com' },
    template_id: 'd-xxxxxxxxxxxxxxxxxxxxxxxx',
  }),
});

// 1. Create template in Mailgun dashboard or via API
// Use {{name}} and {{confirmationCode}} variables

// 2. Send with template name
const formData = new FormData();
formData.append('from', 'noreply@yourdomain.com');
formData.append('to', 'user@example.com');
formData.append('subject', 'Welcome');
formData.append('template', 'welcome-template');
formData.append('h:X-Mailgun-Variables', JSON.stringify({
  name: 'Alice',
  confirmationCode: 'ABC123',
}));

const response = await fetch(
  `https://api.mailgun.net/v3/${env.MAILGUN_DOMAIN}/messages`,
  {
    method: 'POST',
    headers: {
      'Authorization': `Basic ${btoa(`api:${env.MAILGUN_API_KEY}`)}`,
    },
    body: formData,
  }
);

const fileBuffer = await file.arrayBuffer();
const base64Content = btoa(String.fromCharCode(...new Uint8Array(fileBuffer)));

await fetch('https://api.resend.com/emails', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${env.RESEND_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    from: 'noreply@yourdomain.com',
    to: 'user@example.com',
    subject: 'Your Invoice',
    html: '<p>Attached is your invoice.</p>',
    attachments: [{
      filename: 'invoice.pdf',
      content: base64Content,
    }],
  }),
});

const fileBuffer = await file.arrayBuffer();
const base64Content = btoa(String.fromCharCode(...new Uint8Array(fileBuffer)));

const response = await fetch('https://api.sendgrid.com/v3/mail/send', {
  method: 'POST',
  headers: {
    'Authorization': `Bearer ${env.SENDGRID_API_KEY}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    personalizations: [{
      to: [{ email: 'user@example.com' }],
    }],
    from: { email: 'noreply@yourdomain.com' },
    subject: 'Your Invoice',
    content: [{ type: 'text/html', value: '<p>Attached is your invoice.</p>' }],
    attachments: [{
      content: base64Content,
      filename: 'invoice.pdf',
      type: 'application/pdf',
      disposition: 'attachment',
    }],
  }),
});