SendGrid, now part of Twilio, provides email infrastructure for sending marketing and transactional email at scale. The same products, documentation, and resources continue under Twilio.

Email API and SMTP - send transactional and bulk email programmatically or through standard SMTP.
Marketing campaigns - tools for building and sending email campaigns to customers.
Deliverability tooling - documentation, best practices, and support for reaching the inbox.
Twilio platform - combine email with messaging, voice, verification, and customer data products.

It is used by developers and marketers sending application email and campaigns from one provider.

SendGrid offers a free trial with no credit card required, with pricing by volume.