What is Email?

What is email? How does email actually work (simplified)? What are the essential parts of an email address? What is an email client? What is webmail? What's the difference between an email client and webmail? What happens when you press “Send”? How does an email travel from one server to another? What protocols make email work (SMTP, POP, IMAP)? What is the difference between email transport and email storage? What is a mail server? What is the difference between a mail client, a mail server, and an MTA? What is the difference between SMTP, POP3, and IMAP? What is an MUA (Mail User Agent)? What is an MTA (Mail Transfer Agent)? What is an MDA (Mail Delivery Agent)? What is MIME and why does it matter? What is a message header vs. message body? What is plain text vs. HTML email? What is the difference between internal (intranet) email and Internet email? What does “store and forward” mean in email? What is the role of DNS in sending email? What is an MX record and how does it relate to email delivery? What is TLS and how does it secure email in transit? What is the difference between secure submission (587) and relay (25)? How do attachments get encoded in an email? How do images get displayed (linked vs. embedded)? What are headers and why are they important? What is a “Received” header and how do you read it? What is an IP address in the context of email sending? What is the role of reverse DNS (PTR) for email? What is email relay and why is it sometimes abused? What is email forwarding and how does it differ from relaying? What is greylisting and how does it affect email delivery? What is an SMTP handshake? What is the difference between a 2xx, 4xx, and 5xx SMTP response? What is the envelope-from (MAIL FROM) vs. header-from (From:)? What is Return-Path and what does it do? What are common email ports (25, 465, 587, 993, 995)? What is the difference between POP3 and IMAP for retrieving mail? What is a mailbox provider vs. an email service provider (ESP)? What is webmail vs. desktop client vs. mobile app? What is a hosted mailbox? What is an alias vs. a mailbox? What is a distribution list? What is a group mailbox? What is shared mailbox access? What is an email redirect? What is a catch-all mailbox? What is a mailing list manager? What is the role of a spam filter in the mail flow? What happens to an email marked as spam? What is quarantine? What is archiving in email? What happens when an email is deleted? What is an email bounce? (basic definition) What is a delivery receipt vs. read receipt? What is email threading or conversation view? What is CC vs. BCC? What is the difference between BCC and undisclosed recipients? What is the RFC that defines email? What are the size limits for emails? What is encoding (base64, quoted-printable)? What happens when an email is too large? What is a multipart message? What are inline vs. attached images? What is DKIM-Signature header (mention, to link to later section)? What does “Message-ID” mean? What is the difference between a message-ID and a thread-ID? What is an email bounce loop? What is a mail queue? What is a retry schedule? What is an open relay? Why are open relays dangerous? What is email spoofing (brief intro, before deeper section)? What is a spamtrap (brief intro)? What is an autoresponder loop? What is greylisting delay? What is the time-to-deliver metric? What is latency in email? What is store-and-forward reliability? What is the difference between email and chat messaging? What makes email asynchronous communication? Why is email resilient compared to social DMs?