Amazon SES

Amazon SES (Simple Email Service) sends email on behalf of your application. When a shop emails you a receipt, a password reset link or a shipping update, there is a good chance a service like SES is doing the actual sending. Your code hands over the message through an API call or plain SMTP, and SES takes care of delivering it to Gmail, Outlook and every other mailbox.

The hard part of email is not sending it, it is landing in the inbox instead of the spam folder. SES makes you prove you own the sender address or domain, and helps you set up the DNS records that mailbox providers check, such as DKIM and SPF. It also reports bounces (addresses that do not exist) and complaints (people who clicked "this is spam"), so you can stop writing to them.

New accounts start in a sandbox: you can only send to addresses you have verified, with a small daily limit, until you ask AWS for production access. After that the price is roughly ten cents per thousand emails. If your bounce or complaint rates climb too high, AWS can pause your sending to protect everyone else's reputation, so keeping your mailing lists clean is part of the job.