Email Delivery Flow

email-delivery-flow.md

Generated using ChatGPT with reference image from https://www.youtube.com/watch?v=cjPVlxmf_Vk

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🔠 Abbreviations and Their Full Forms

• MUA – Mail User Agent (e.g., Outlook, Apple Mail)
• MSA – Mail Submission Agent
• MTA – Mail Transfer Agent
• MDA – Mail Delivery Agent
• SMTP – Simple Mail Transfer Protocol
• POP3 – Post Office Protocol version 3
• IMAP – Internet Message Access Protocol

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📥 Flow Summary: Email from Sender to Receiver

1. Sender Side (Client + Mail Server)

• The user writes and sends an email using the MUA (e.g., Outlook, Apple Mail).
• MUA sends the email via SMTP to the MSA.
• MSA validates, formats, and forwards the message to the MTA.
• MTA handles the actual routing of the email using SMTP to deliver it to the recipient’s mail server.

2. Receiver Side (Mail Server + Client)

• The receiver's MTA receives the mail and passes it on to the MDA.
• MDA stores the email into the recipient’s mailbox.
• The POP3/IMAP server fetches the stored email.
• The receiver’s MUA (again, e.g., Outlook, Apple Mail) pulls the email via POP3 or IMAP.

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✅ Protocol Roles

• SMTP: Used to send mail between servers and from client to server.
• POP3/IMAP: Used by the receiving MUA to retrieve the mail from the server.

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💡 Conceptual Summary

It's a store-and-forward system:

• Email is composed and sent via MUA.
• Routed through a series of agents (MSA → MTA → MDA).
• Stored in a mailbox on the receiving server.
• Retrieved later by the recipient’s MUA via POP3/IMAP.