Part 1: Mail Server Communications 101

Sun, 01 Mar 2026 23:21:21 +0530

This guide explains the core building blocks required to send and receive email via the internet. It focuses on a understanding how the email is sent across the real world and what protocols are used within this communication.

The Components of a Mail Communication Link to heading

DNS Server: Routes trusted servers, handles MX / SPF / DKIM records for mail delivery and authority verification.
Mail Servers: Receives outbound emails from clients and moves messages across each other using SMTP.
Mail Client: Applications used by people to send / receive emails (eg. Outlook, Thunderbird).

Mail Server Communication Model

Mail flow Link to heading

You write an email on thunderbird and press Send.
Your mail client submits it to your mail server using SMTP (port 587).
Your mail server checks the recipient’s domain.
It queries DNS to find the domain’s MX record.
DNS tells your server which mail server handles that domain.
Your server connects to the recipient’s server using SMTP (port 25).
The recipient server verifies security (SPF/DKIM/TLS).
If valid, it accepts and stores the email.
The recipient’s mail client connects via IMAP (993) or POP3 (995).
The email appears in their inbox.

1. DNS Server Link to heading

Before email works, the internet must know which server handles mail for a particular domain, where that server is located and whether that server is trusted. This is handled through DNS (Domain Name System).

POP3 on DevLogs

Part 1: Mail Server Communications 101

The Components of a Mail Communication Link to heading

Mail flow Link to heading

1. DNS Server Link to heading