There are a lot of mailer services out there, mailgun and SendGrid being two of them (disclaimer: Iʼm a user of both services).
SMTP is a good thing, if you have an in-house SMTP server that you can use for this. However, setting up an SMTP server is a real burden, especially if you want to do it right, so a lot of sites use such mailing services.
If I were you, I would go and discover these services to find which one fits the needs of the projects best.