Amazon SES API
Amazon Simple Email Service — a highly scalable, low-cost email sending API for transactional, marketing, and bulk email with SMTP and REST interfaces.
ZeroBounce
Email validation and deliverability API that verifies email addresses in real-time or in batch, scoring them on validity, bounce risk, spam traps, and abuse patterns.
NeverBounce
Email verification service that validates individual emails in real-time or processes large lists in bulk, providing bounce prediction and deliverability scores for email marketing hygiene.
ConvertKit (Kit)
Email marketing platform built for creators and online businesses, with subscriber tagging, automation sequences, and a REST API for managing subscribers, forms, sequences, and broadcasts programmatically.
SparkPost (Bird) API
SparkPost (now part of Bird) email delivery API for transactional and marketing email with advanced deliverability analytics, SMTP relay, and recipient validation.
Mailchimp
Email marketing platform with audience management, campaign creation, and marketing automation, offering a REST API for programmatic list management, campaign sending, and analytics retrieval.