Resend MCP Server

Instructions

Implementation Reference

• src/index.ts:75-108 (handler)

  Handler for 'resend_send_email' tool: parses arguments with SendEmailRequestSchema, builds Resend email options, sends email, returns success with ID.

  case 'resend_send_email': {
    const args = SendEmailRequestSchema.parse(request.params.arguments);
  
    // Build email options - Resend requires html or text
    const emailOptions: Parameters<typeof resend.emails.send>[0] = {
      from: fromEmail,
      to: args.to,
      subject: args.subject,
      ...(args.html ? { html: args.html } : { text: args.text! }),
      ...(args.cc && { cc: args.cc }),
      ...(args.bcc && { bcc: args.bcc }),
      ...(args.reply_to && { replyTo: args.reply_to }),
      ...(args.tags && { tags: args.tags }),
    };
  
    const { data, error } = await resend.emails.send(emailOptions);
  
    if (error) {
      throw new Error(`Failed to send email: ${error.message}`);
    }
  
    return {
      content: [
        {
          type: 'text',
          text: JSON.stringify({
            success: true,
            id: data?.id,
            message: 'Email sent successfully',
          }),
        },
      ],
    };
  }

• src/schemas.ts:18-50 (schema)

  Input schema (Zod) for the resend_send_email tool defining parameters like to, subject, html/text, cc, bcc, etc.

  export const SendEmailRequestSchema = z
    .object({
      to: z
        .union([z.string().email(), z.array(z.string().email()).max(50)])
        .describe('Recipient email address(es). Max 50 addresses.'),
      subject: z.string().describe('Email subject line'),
      html: z.string().optional().describe('HTML version of the email body'),
      text: z
        .string()
        .optional()
        .describe('Plain text version. Auto-generated from HTML if omitted.'),
      cc: z
        .union([z.string().email(), z.array(z.string().email())])
        .optional()
        .describe('CC recipient(s)'),
      bcc: z
        .union([z.string().email(), z.array(z.string().email())])
        .optional()
        .describe('BCC recipient(s)'),
      reply_to: z
        .union([z.string().email(), z.array(z.string().email())])
        .optional()
        .describe('Reply-to email address(es)'),
      tags: z
        .array(TagSchema)
        .max(50)
        .optional()
        .describe('Custom metadata tags for tracking (max 50)'),
    })
    .refine((data) => data.html || data.text, {
      message: 'Either html or text must be provided',
      path: ['html', 'text'],
    });

• src/index.ts:52-56 (registration)

  Tool registration in the MCP server: defines name, description, and inputSchema for listTools.

  {
    name: 'resend_send_email',
    description:
      'Send a single email to one or more recipients. Supports HTML and plain text content, CC/BCC, reply-to, and custom tags for tracking.',
    inputSchema: zodToJsonSchema(SendEmailRequestSchema),