Connect Microsoft 365 & Outlook: Enterprise Sales Email & Graph API

private async getAccessToken(): Promise<string | null> {
  if (!this.refreshToken || !this.clientId || !this.clientSecret) {
    return null;
  }

  try {
    const res = await fetch(`https://login.microsoftonline.com/${this.tenantId}/oauth2/v2.0/token`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
      body: new URLSearchParams({
        client_id: this.clientId,
        client_secret: this.clientSecret,
        refresh_token: this.refreshToken,
        grant_type: 'refresh_token',
        scope: 'https://graph.microsoft.com/Mail.Send https://graph.microsoft.com/Mail.ReadWrite offline_access',
      }).toString(),
    });

    if (!res.ok) return null;
    const data: any = await res.json().catch(() => ({}));
    return data?.access_token || null;
  } catch {
    return null;
  }
}

const payload: any = {
  message: {
    subject: options.subject,
    body: {
      contentType: 'HTML',
      content: options.htmlContent,
    },
    toRecipients: options.to.map((t) => ({
      emailAddress: { address: t.email, name: t.name || t.email.split('@')[0] },
    })),
    from: {
      emailAddress: { address: options.fromEmail, name: options.fromName },
    },
  },
  saveToSentItems: 'true',
};

const res = await fetch('https://graph.microsoft.com/v1.0/me/sendMail', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${token}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify(payload),
});