This book is a collection of notes and sample codes written by the author while he was learning email systems. Topics include email message transmission protocols: SMTP, IMAP, POP3; secure connections with SSL/TLS protocols; managing Postfix server as MSA, MTA and MDA agents; managing Dovecot server for email retrieval with IMAP and POP3 protocols; Thunderbird and other email client tools; using PHPMailer to send emails in PHP scripts; email message format and headers. Updated in 2024 (Version v1.04) with PHPMailer tutorials. For latest updates and free sample chapters, visit https://www.herongyang.com/Email.