Follow one email from Alice’s laptop to Bob’s phone — and name the protocol at every box.
This box is the destination of the whole SMTP journey — not Bob’s phone.
- who moves mail between servers
- SMTP · 587 then 25
- who takes it out of the mailbox
- IMAP · 143 or 993
- where the mailbox lives
- the server
- what the second device sees
- — not checked yet —
always — push only, never pulls anything
143 is the original plaintext port; 993 is the same IMAP wrapped in TLS — pull only, it cannot send
devices hold copies of it
run the journey to the laptop step
Nothing has left Alice’s laptop yet. What has to happen before any protocol gets involved?
Three protocols, three jobs. SMTP carries the mail from Alice as far as Bob’s server and stops. Then IMAP or POP3 — Bob’s choice — gets it out of the mailbox and onto his screen. Press Send and watch each box light up.
“Email is one protocol.” It is three jobs. SMTP pushes mail towards a mailbox. IMAP or POP3 pulls it out of one. No protocol does both.
“SMTP delivers to Bob.” SMTP stops at Bob’s server. His phone was offline the whole time and nothing waited for it.
“POP3 always deletes downloaded mail.” It does not. RETR downloads; DELE marks a message for removal, and QUIT commits that removal. This demo deliberately shows delete-after-download. IMAP additionally provides server-side folders and shared state across devices.
Follow one email from Alice’s laptop to Bob’s phone — and name the protocol at every box.
- Which protocol delivers the mail into Bob’s mailbox?
- Why does the laptop already show the mail as read?
Read it now and keep it in mind — the answer is in what you are about to watch.