Amazon SES
https://aws.amazon.com/ses/pricing
Sending email from an application hosted in EC2
$0 for the first 62,000 emails sent per month, and $0.10 per 1,000 emails sent thereafter.
Sending email from an email client or other software package
Q: Does Amazon SES provide an SMTP endpoint?
Amazon SES provides an SMTP interface for seamless integration with applications that can send email via SMTP. You can connect directly to this SMTP interface from your applications, or configure your existing email server to use this interface as an SMTP relay.