📚 smtp - Awesome Go Library for Email

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SMTP server protocol state machine.

🏷️ Email
📂 Libraries and tools that implement email creation and sending.
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Detailed Description of smtp

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.

HookDescription
LogHandlerCalled for every log message
MessageReceivedHandlerCalled for each message received
ValidateSenderHandlerCalled after MAIL FROM
ValidateRecipientHandlerCalled after RCPT TO
ValidateAuthenticationHandlerCalled after AUTH
SMTPVerbFilterCalled for every SMTP command processed
TLSHandlerCallback mashup called after STARTTLS
GetAuthenticationMechanismsHandlerCalled for each EHLO command

Behaviour flags

The state machine also exports variables to control its behaviour:

See GoDoc for more information.

VariableDescription
RejectBrokenRCPTSyntaxReject non-conforming RCPT syntax
RejectBrokenMAILSyntaxReject non-conforming MAIL syntax
RequireTLSRequire STARTTLS before other commands
MaximumRecipientsMaximum recipients per message
MaximumLineLengthMaximum length of SMTP line

Licence

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

Released under MIT license, see LICENSE for details.