Companies like Mailchimp and MailerLite are email marketing software options that help you build marketing emails through their system. However, these companies only allow you to send bulk emails, not individual (or transactional) emails to individual users.
Amazon's Simple Email Service and SendGrid are actually SMTP service providers, meaning they allow you to send transactional and bulk emails. You will need to use your own email marketing software to make use of these services though.