No server side code required to send email at all.
Firebase Cloud Messaging (FCM) is a cross-platform messaging solution that lets you reliably deliver messages at no cost.
Email sending service.
For sending Android, iOS, and Web push notifications.
Transactional email sending service.
Email sending service. Has an email builder tool as well.
Email sending service with analytics.
Twilio offers powerful APIs for text messaging, voice, and video.