SMTP Reference

Holamail implements a basic plain-SMTP listener. It accepts SMTP messages and logs them; it does not deliver mail externally.

Connection

Public test host:

1telnet smtp.testmail.hola.cloud 25

Local instance:

1telnet localhost 2525

STARTTLS and SMTP AUTH are not supported.

SMTP Commands

HELO / EHLO

Initiate the SMTP session.

1EHLO client.example.com

Typical response:

1250 Hello client.example.com

MAIL FROM

Specify the sender address.

1MAIL FROM:<noreply@example.com>

Typical response:

1250 OK

RCPT TO

Specify a recipient address.

1RCPT TO:<user@example.com>

Typical response:

1250 OK

DATA

Begin the message content. End with a line containing only a period (.).

1DATA

Typical response:

1354 End data with <CR><LF>.<CR><LF>

Then send headers and body:

1From: noreply@example.com
2To: user@example.com
3Subject: Holamail test
4
5This message will be logged by Holamail.
6.

Typical response:

1250 OK

QUIT

Terminate the SMTP session.

1QUIT

Typical response:

1221 Bye

Full SMTP Session Example

1printf 'EHLO client.example.com\r\nMAIL FROM:<noreply@example.com>\r\nRCPT TO:<user@example.com>\r\nDATA\r\nFrom: noreply@example.com\r\nTo: user@example.com\r\nSubject: Test\r\n\r\nHello!\r\n.\r\nQUIT\r\n' | nc localhost 2525

Example Go Code

 1package main
 2
 3import (
 4    "log"
 5    "net/smtp"
 6)
 7
 8func main() {
 9    from := "noreply@example.com"
10    to := []string{"user@example.com"}
11    msg := []byte("From: noreply@example.com\r\n" +
12        "To: user@example.com\r\n" +
13        "Subject: Holamail test\r\n\r\n" +
14        "This message will be logged by Holamail.\r\n")
15
16    if err := smtp.SendMail("smtp.testmail.hola.cloud:25", nil, from, to, msg); err != nil {
17        log.Fatal(err)
18    }
19}

Error Codes

Scope

Holamail logs accepted messages only. It does not include external delivery, HTTP APIs, STARTTLS, AUTH, rate limiting, templates, analytics, or tracking.