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Zapmail processes incoming emails through a custom SMTP server and displays them in a web interface. This page explains the complete email flow from reception to viewing.

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Email flow overview

1

SMTP server receives email

When someone sends an email to username@zapmail.parth.lol, it arrives at Zapmail’s custom SMTP server running on Go. The server accepts the connection and responds with a greeting:
220 Welcome to Temporary Mail Service
2

SMTP handshake

The SMTP server processes standard SMTP commands in sequence:
  • HELO or EHLO - Establishes the connection
  • MAIL FROM - Identifies the sender
  • RCPT TO - Specifies the recipient (e.g., <username@zapmail.parth.lol>)
  • DATA - Indicates the start of the email content
3

Email data collection

After receiving the DATA command, the server collects all email content line by line until it encounters a single period (.) on a line by itself. This raw email data includes:
  • Email headers (From, To, Subject, Date, etc.)
  • MIME parts and content-type information
  • HTML and plain text body content
  • Any attachments or embedded images
4

Username extraction

The server extracts the username from the recipient address by:
  1. Removing angle brackets (< and >)
  2. Splitting on the @ symbol
  3. Taking the first part as the username
For example, <john@zapmail.parth.lol> becomes john.
5

Database storage

The email is stored in a PostgreSQL (Supabase) database with the following information:
  • username - The extracted username portion
  • recipient - The full recipient address with angle brackets
  • raw_data - The complete raw email content
  • received_at - Timestamp of when the email was received
6

Web interface retrieval

When you visit your inbox at /user?q=username, the web application:
  1. Queries the database for all emails where recipient = <username@zapmail.parth.lol>
  2. Parses each raw email using the mailparser library
  3. Extracts structured data (subject, from, body, attachments, date)
  4. Displays emails in reverse chronological order (newest first)

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Technical architecture

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SMTP server (Go)

The backend SMTP server handles concurrent connections using goroutines. Each incoming connection is processed independently: 
for {
    conn, err := ln.Accept()
    if err != nil {
        log.Println("Error accepting connection:", err)
        continue
    }
    go handleConnection(conn, db)
}
The server supports multiple simultaneous email deliveries without blocking, making it efficient for handling high volumes of incoming mail.

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Email parsing

Raw email data is stored as-is in the database. When you access your inbox, the Next.js application parses the raw email to extract:
  • Subject line - The email’s subject
  • From address - Sender’s email address and name
  • Date - When the email was sent
  • Text content - Plain text version of the email body
  • HTML content - Rich HTML version for display
  • Attachments - Any files attached to the email
This separation allows the SMTP server to remain lightweight and fast, while the web interface handles the complex parsing logic.

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Supported SMTP commands

Zapmail’s SMTP server implements the following commands:
  • HELO / EHLO - Identify the client to the server
  • MAIL FROM - Specify the sender’s email address
  • RCPT TO - Specify the recipient’s email address
  • DATA - Begin transmission of email content
  • QUIT - Close the connection
  • NOOP - No operation (keeps connection alive)
  • HELP - Lists supported commands
  • VRFY - Verify an email address (returns “not supported”)
  • EXPN - Expand a mailing list (returns “not supported”)
Any unrecognized SMTP command receives a 500 Unrecognized command response, ensuring compatibility with standard SMTP clients.

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Response codes

The SMTP server uses standard response codes:
  • 220 - Service ready (initial greeting)
  • 250 - Requested action completed successfully
  • 354 - Start mail input (after DATA command)
  • 221 - Service closing connection (after QUIT)
  • 500 - Command not recognized
  • 550 - Error (e.g., failed to store email)
These codes ensure compatibility with all standard email clients and services.

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