MailHog SMTP Protocol

MailHog SMTP Protocol GoDoc Build Status

github.com/mailhog/smtp implements an SMTP server state machine.

It attempts to encapsulate as much of the SMTP protocol (plus its extensions) as possible without compromising configurability or requiring specific backend implementations.

proto := NewProtocol()
reply := proto.Start()
reply = proto.ProcessCommand("EHLO localhost")
// ...

See MailHog-Server and MailHog-MTA for example implementations.

Commands and replies

Interaction with the state machine is via:

  • the Parse function
  • the ProcessCommand and ProcessData functions

You can mix the use of all three functions as necessary.

Parse

Parse should be used on a raw text stream. It looks for an end of line (\r\n), and if found, processes a single command. Any unprocessed data is returned.

If any unprocessed data is returned, Parse should be called again to process then next command.

text := "EHLO localhost\r\nMAIL FROM:<test>\r\nDATA\r\nTest\r\n.\r\n"

var reply *smtp.Reply
for {
  text, reply = proto.Parse(text)
  if len(text) == 0 {
    break
  }
}

ProcessCommand and ProcessData

ProcessCommand should be used for an already parsed command (i.e., a complete SMTP "line" excluding the line ending).

ProcessData should be used if the protocol is in DATA state.

reply = proto.ProcessCommand("EHLO localhost")
reply = proto.ProcessCommand("MAIL FROM:<test>")
reply = proto.ProcessCommand("DATA")
reply = proto.ProcessData("Test\r\n.\r\n")

Hooks

The state machine provides hooks to manipulate its behaviour.

See GoDoc for more information.

Hook Description
LogHandler Called for every log message
MessageReceivedHandler Called for each message received
ValidateSenderHandler Called after MAIL FROM
ValidateRecipientHandler Called after RCPT TO
ValidateAuthenticationHandler Called after AUTH
SMTPVerbFilter Called for every SMTP command processed
TLSHandler Callback mashup called after STARTTLS
GetAuthenticationMechanismsHandler Called for each EHLO command

Behaviour flags

The state machine also exports variables to control its behaviour:

See GoDoc for more information.

Variable Description
RejectBrokenRCPTSyntax Reject non-conforming RCPT syntax
RejectBrokenMAILSyntax Reject non-conforming MAIL syntax
RequireTLS Require STARTTLS before other commands
MaximumRecipients Maximum recipients per message
MaximumLineLength Maximum length of SMTP line

Licence

Copyright ©‎ 2014-2015, Ian Kent (http://iankent.uk)

Released under MIT license, see LICENSE for details.

Owner
MailHog
Web and API based SMTP testing
MailHog
https://github.com/mailhog/smtp
Comments
  • scripted telnet doesn't work

    scripted telnet doesn't work 

    telnet 127.0.0.1 25 << EOF
HELO cloudflare.com
MAIL FROM:<[email protected]>
RCPT TO:<[email protected]>
DATA
Body of email.
.
QUIT
EOF

    I tested this with postfix and other mtas with no issues.

  • support MAIL command with a null

    support MAIL command with a null

    MAIL command with a null is required in rfc5321 as shown below.

    https://tools.ietf.org/html/rfc5321#section-3.6.3

    One way to prevent loops in error reporting is to specify a null reverse-path
in the MAIL command of a notification message.
When such a message is transmitted, the reverse-path MUST be set to null
(see   Section 4.5.5 for additional discussion).
A MAIL command with a null reverse-path appears as follows:

  MAIL FROM:<>

    In fact, Postfix bounce emails have MAIL command set to "FROM:<>". But, MailHog validation judges "FROM:<>" as an error. Therefore, Postfix bounce email cannot be received by MailHog.

    This Pull Request allows you to receive Postfix bounce email by support MAIL command with a null.

  • RSET clears EHLO

    RSET clears EHLO

    When issuing a RSET command, mailhog will reset the SMTPMessage. This will also clear the original Helo value. Since a "real" mail server will usually keep the smtp HELO value intact, would it be worthwhile to also have that behaviour here?

    https://github.com/mailhog/smtp/blob/0c4e9b7e0625fec61d0c30d7b2f6c62852be6c54/protocol.go#L233

  • Is this abandoned?

    Is this abandoned?

    I've had an open issue (#2), and two open PRs (#3, #4) for over a year, now, with no response here. Is there any hope the changes will ever be responded to?

  • Hooks for SMTP extensions

    Hooks for SMTP extensions

    It would be really useful if SMTP extensions could be supported. This would include replying with the added SMTP extensions in the EHLO response, and providing hooks so extensions can add functionality.

    I'm attempting to support the SMTP Extensions for Internationalized Email (RFC 6531), but that's not possible with the current implementation.

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