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The Zapmail SMTP server implements standard SMTP protocol commands for receiving email messages.

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Supported commands

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HELO

Initiates an SMTP session with the server. Syntax: HELO <domain> Response: 250 Hello Example: 
HELO example.com
250 Hello

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EHLO

Extended SMTP greeting command. Functions identically to HELO in the current implementation. Syntax: EHLO <domain> Response: 250 Hello Example: 
EHLO example.com
250 Hello

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MAIL FROM

Specifies the sender’s email address for the message. Syntax: MAIL FROM:<sender@example.com> Response: 250 Sender OK Example: 
MAIL FROM:<sender@example.com>
250 Sender OK

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RCPT TO

Specifies the recipient’s email address. The server extracts the username portion and stores it for the email record. Syntax: RCPT TO:<recipient@zapmail.parth.lol> Response: 250 Recipient OK Example: 
RCPT TO:<user@zapmail.parth.lol>
250 Recipient OK

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DATA

Initiates the message data transfer. The server accepts all lines until a line containing only a period (.) is received. Syntax: DATA Response: 354 End data with <CR><LF>.<CR><LF> After data is received:
  • Success: 250 OK: Message accepted
  • Error: 550 Error storing email
Example: 
DATA
354 End data with <CR><LF>.<CR><LF>
Subject: Test Email
From: sender@example.com
To: user@zapmail.parth.lol

This is the message body.
.
250 OK: Message accepted

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QUIT

Closes the SMTP session and disconnects. Syntax: QUIT Response: 221 Bye Example: 
QUIT
221 Bye

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NOOP

No operation command. The server acknowledges but performs no action. Syntax: NOOP Response: 250 OK Example: 
NOOP
250 OK

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VRFY

Verify command. Not supported by the Zapmail server. Syntax: VRFY Response: 250 VRFY not supported

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EXPN

Expand command. Not supported by the Zapmail server. Syntax: EXPN Response: 250 EXPN not supported

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HELP

Displays a list of supported commands. Syntax: HELP Response: 
214-Commands supported:
214 HELO, EHLO, MAIL FROM, RCPT TO, DATA, NOOP, VRFY, HELP, EXPN, QUIT

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Implementation details

The SMTP command handler is implemented in backend/main.go:92-158. Commands are case-insensitive and processed in a continuous loop until the client issues QUIT or disconnects.

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Greeting message

When a client connects, the server sends: 
220 Welcome to Temporary Mail Service

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Unrecognized commands

Any command not listed above will receive: 
500 Unrecognized command