In this chapter, we looked at how email is delivered over the internet. SMTP, the protocol responsible for email delivery, was studied in some depth. We then constructed a simple program to send short emails using SMTP.

We looked at the email format too. We saw how MIME could be used to send multipart emails with file attachments.

We also saw how sending emails over the modern internet is full of pitfalls. Many of these stems from attempts to block spam. Techniques used by providers, such as blocking residential IP addresses, SPF, DKIM, DMARC, and IP address reputation monitoring, may make it difficult for our simple program to deliver email reliably.

In the next chapter, Chapter 9, Loading Secure Web Pages with HTTPS and OpenSSL, we look at secure web connections using HTTPS.