smtpmock is lightweight configurable multithreaded fake SMTP server written in Go. It meets the minimum requirements specified by RFC 2821 & RFC 5321. Allows to mimic any SMTP server behavior for your test environment and even more 🚀

Features

Configurable multithreaded RFC compatible SMTP server
Implements the minimum command set, responds to commands and adds a valid received header to messages as specified in RFC 2821 & RFC 5321
Ability to configure behavior for each SMTP command
Comes with default settings out of the box, configure only what you need
Ability to override previous SMTP commands
Fail fast scenario (ability to close client session for case when command was inconsistent or failed)
Multiple receivers (ability to configure multiple RCPT TO commands receiving during one session)
Multiple message receiving (ability to configure multiple message receiving during one session)
Mock-server activity logger
Ability to do graceful/force shutdown of SMTP mock server
No authentication support
Zero runtime dependencies
Ability to access to server messages
Simple and intuitive DSL
Ability to run server as binary with command line arguments

Requirements

Golang 1.15+

Installation

Install smtpmock:

go get github.com/mocktools/go-smtp-mock/v2
go install github.com/mocktools/go-smtp-mock/v2

Import smtpmock dependency into your code:

package main

import smtpmock "github.com/mocktools/go-smtp-mock/v2"

Usage

Inside of Golang ecosystem
- Configuring
- Manipulation with server
Inside of Ruby ecosystem
- Example of usage
Inside of any ecosystem
Implemented SMTP commands

Inside of Golang ecosystem

You have to create your SMTP mock server using smtpmock.New() and smtpmock.ConfigurationAttr{} to start interaction with it.

Configuring

smtpmock is SMTP server for test environment with configurable behavior. It comes with default settings out of the box. But you can override any default behavior if you need.

smtpmock.ConfigurationAttr{

  // Customizing server behavior
  // ---------------------------------------------------------------------
  // Host address where smtpmock will run, it's equal to "127.0.0.1" by default
  HostAddress:                   "[::]",

  // Port number on which the server will bind. If it not specified, it will be
  // assigned dynamically after server.Start() by default
  PortNumber:                    2525,

  // Enables/disables log to stdout. It's equal to false by default
  LogToStdout:                   true,

  // Enables/disables log server activity. It's equal to false by default
  LogServerActivity:             true,

  // Ability to specify session timeout. It's equal to 30 seconds by default
  SessionTimeout:                42,

  // Ability to specify graceful shutdown timeout. It's equal to 1 second by default
  ShutdownTimeout:               5,


  // Customizing SMTP command handlers behavior
  // ---------------------------------------------------------------------
  // Ability to configure fail fast scenario. It means that server will
  // close client session for case when command was inconsistent or failed.
  // It's equal to false by default
  IsCmdFailFast:                 true,

  // Ability to configure multiple RCPT TO command receiving during one session.
  // It means that server will handle and save all RCPT TO command request-response
  // pairs until receive successful response and next SMTP command has been passed.
  // Please note, by default will be saved only one, the last RCPT TO command
  // request-response pair. It's equal to false by default
  MultipleRcptto:                true,

  // Ability to configure multiple message receiving during one session. It means that server
  // will create another message during current SMTP session in case when RSET
  // command has been used after successful commands chain: MAIL FROM, RCPT TO, DATA.
  // Please note, by default RSET command flushes current message in any case.
  // It's equal to false by default
  MultipleMessageReceiving:      true,

  // Ability to specify blacklisted HELO domains. It's equal to empty []string
  BlacklistedHeloDomains:        []string{"example1.com", "example2.com", "localhost"},

  // Ability to specify blacklisted MAIL FROM emails. It's equal to empty []string
  BlacklistedMailfromEmails:     []string{"bot@olo.com", "robot@molo.com"},

  // Ability to specify blacklisted RCPT TO emails. It's equal to empty []string
  BlacklistedRcpttoEmails:       []string{"blacklisted@olo.com", "blacklisted@molo.com"},

  // Ability to specify not registered (non-existent) RCPT TO emails.
  // It's equal to empty []string
  NotRegisteredEmails:           []string{"nobody@olo.com", "non-existent@email.com"},

  // Ability to specify HELO response delay in seconds. It runs immediately,
  // equals to 0 seconds by default
  ResponseDelayHelo:             2,

  // Ability to specify MAIL FROM response delay in seconds. It runs immediately,
  // equals to 0 seconds by default
  ResponseDelayMailfrom:         2,

  // Ability to specify RCPT TO response delay in seconds. It runs immediately,
  // equals to 0 seconds by default
  ResponseDelayRcptto:           2,

  // Ability to specify DATA response delay in seconds. It runs immediately,
  // equals to 0 seconds by default
  ResponseDelayData:             2,

  // Ability to specify message response delay in seconds. It runs immediately,
  // equals to 0 seconds by default
  ResponseDelayMessage:          2,

  // Ability to specify RSET response delay in seconds. It runs immediately,
  // equals to 0 seconds by default
  ResponseDelayRset:             2,

  // Ability to specify QUIT response delay in seconds. It runs immediately,
  // equals to 0 seconds by default
  ResponseDelayQuit:             2,

  // Ability to specify message body size limit. It's equal to 10485760 bytes (10MB) by default
  MsgSizeLimit:                  5,


  // Customizing SMTP command handler messages context
  // ---------------------------------------------------------------------
  // Custom server greeting message. Base on defaultGreetingMsg by default
  MsgGreeting:                   "msgGreeting",

  // Custom invalid command message. Based on defaultInvalidCmdMsg by default
  MsgInvalidCmd:                 "msgInvalidCmd",

  // Custom invalid command HELO sequence message.
  // Based on defaultInvalidCmdHeloSequenceMsg by default
  MsgInvalidCmdHeloSequence:     "msgInvalidCmdHeloSequence",

  // Custom invalid command HELO argument message.
  // Based on defaultInvalidCmdHeloArgMsg by default
  MsgInvalidCmdHeloArg:          "msgInvalidCmdHeloArg",

  // Custom HELO blacklisted domain message. Based on defaultQuitMsg by default
  MsgHeloBlacklistedDomain:      "msgHeloBlacklistedDomain",

  // Custom HELO received message. Based on defaultReceivedMsg by default
  MsgHeloReceived:               "msgHeloReceived",

  // Custom invalid command MAIL FROM sequence message.
  // Based on defaultInvalidCmdMailfromSequenceMsg by default
  MsgInvalidCmdMailfromSequence: "msgInvalidCmdMailfromSequence",

  // Custom invalid command MAIL FROM argument message.
  // Based on defaultInvalidCmdMailfromArgMsg by default
  MsgInvalidCmdMailfromArg:      "msgInvalidCmdMailfromArg",

  // Custom MAIL FROM blacklisted email message. Based on defaultQuitMsg by default
  MsgMailfromBlacklistedEmail:   "msgMailfromBlacklistedEmail",

  // Custom MAIL FROM received message. Based on defaultReceivedMsg by default
  MsgMailfromReceived:           "msgMailfromReceived",

  // Custom invalid command RCPT TO sequence message.
  // Based on defaultInvalidCmdRcpttoSequenceMsg by default
  MsgInvalidCmdRcpttoSequence:   "msgInvalidCmdRcpttoSequence",

  // Custom invalid command RCPT TO argument message.
  // Based on defaultInvalidCmdRcpttoArgMsg by default
  MsgInvalidCmdRcpttoArg:        "msgInvalidCmdRcpttoArg",

  // Custom RCPT TO not registered email message.
  // Based on defaultNotRegisteredRcpttoEmailMsg by default
  MsgRcpttoNotRegisteredEmail:   "msgRcpttoNotRegisteredEmail",

  // Custom RCPT TO blacklisted email message. Based on defaultQuitMsg by default
  MsgRcpttoBlacklistedEmail:     "msgRcpttoBlacklistedEmail",

  // Custom RCPT TO received message. Based on defaultReceivedMsg by default
  MsgRcpttoReceived:             "msgRcpttoReceived",

  // Custom invalid command DATA sequence message.
  // Based on defaultInvalidCmdDataSequenceMsg by default
  MsgInvalidCmdDataSequence:     "msgInvalidCmdDataSequence",

  // Custom DATA received message. Based on defaultReadyForReceiveMsg by default
  MsgDataReceived:               "msgDataReceived",

  // Custom size is too big message. Based on defaultMsgSizeIsTooBigMsg by default
  MsgMsgSizeIsTooBig:            "msgMsgSizeIsTooBig",

  // Custom received message body message. Based on defaultReceivedMsg by default
  MsgMsgReceived:                "msgMsgReceived",

  // Custom invalid command RSET sequence message.
  // Based on defaultInvalidCmdHeloSequenceMsg by default
  MsgInvalidCmdRsetSequence:     "msgInvalidCmdRsetSequence",

  // Custom invalid command RSET message. Based on defaultInvalidCmdMsg by default
  MsgInvalidCmdRsetArg:           "msgInvalidCmdRsetArg",

  // Custom RSET received message. Based on defaultOkMsg by default
  MsgRsetReceived:               "msgRsetReceived",

  // Custom quit command message. Based on defaultQuitMsg by default
  MsgQuitCmd:                    "msgQuitCmd",
}

Manipulation with server

package main

import (
  "fmt"
  "net"
  "net/smtp"

  smtpmock "github.com/mocktools/go-smtp-mock/v2"
)

func main() {
  // You can pass empty smtpmock.ConfigurationAttr{}. It means that smtpmock will use default settings
  server := smtpmock.New(smtpmock.ConfigurationAttr{
    LogToStdout:       true,
    LogServerActivity: true,
  })

  // To start server use Start() method
  if err := server.Start(); err != nil {
    fmt.Println(err)
  }

  // Server's port will be assigned dynamically after server.Start()
  // for case when portNumber wasn't specified
  hostAddress, portNumber := "127.0.0.1", server.PortNumber()

  // Possible SMTP-client stuff for iteration with mock server
  address := fmt.Sprintf("%s:%d", hostAddress, portNumber)
  timeout := time.Duration(2) * time.Second

  connection, _ := net.DialTimeout("tcp", address, timeout)
  client, _ := smtp.NewClient(connection, hostAddress)
  client.Hello("example.com")
  client.Quit()
  client.Close()

  // Each result of SMTP session will be saved as message.
  // To get access to server messages use Messages() method
  server.Messages()

  // To stop the server use Stop() method. Please note, smtpmock uses graceful shutdown.
  // It means that smtpmock will end all sessions after client responses or by session
  // timeouts immediately.
  if err := server.Stop(); err != nil {
    fmt.Println(err)
  }
}

Code from example above will produce next output to stdout:

INFO: 2021/11/30 22:07:30.554827 SMTP mock server started on port: 2525
INFO: 2021/11/30 22:07:30.554961 SMTP session started
INFO: 2021/11/30 22:07:30.554998 SMTP response: 220 Welcome
INFO: 2021/11/30 22:07:30.555059 SMTP request: EHLO example.com
INFO: 2021/11/30 22:07:30.555648 SMTP response: 250 Received
INFO: 2021/11/30 22:07:30.555686 SMTP request: QUIT
INFO: 2021/11/30 22:07:30.555722 SMTP response: 221 Closing connection
INFO: 2021/11/30 22:07:30.555732 SMTP session finished
WARNING: 2021/11/30 22:07:30.555801 SMTP mock server is in the shutdown mode and won't accept new connections
INFO: 2021/11/30 22:07:30.555808 SMTP mock server was stopped successfully

Inside of Ruby ecosystem

In Ruby ecosystem smtpmock is available as smtp_mock gem. It's flexible Ruby wrapper over smtpmock binary.

Example of usage

First, you should install smtp_mock gem and smtpmock as system dependency:

gem install smtp_mock
bundle exec smtp_mock -i ~

Now, you can create and interact with your smtpmock instance natively from Ruby ecosystem. It comes with default settings out of the box. Configure only what you need, for example:

require 'smtp_mock'

# List of all available server options:
# https://github.com/mocktools/ruby-smtp-mock#available-server-options
smtp_mock_server = SmtpMock.start_server(not_registered_emails: %w[user@olo.com user@molo.com])

# returns current smtp mock server port
smtp_mock_server.port # => 55640

# interface for force shutdown current smtp mock server
smtp_mock_server.stop! # => true

Inside of any ecosystem

You can use smtpmock as binary. Just download the pre-compiled binary from the releases page and copy them to the desired location. For start server run command with needed arguments. You can use our bash script for automation this process like in the example below:

curl -sL https://raw.githubusercontent.com/mocktools/go-smtp-mock/master/script/download.sh | bash
./smtpmock -port=2525 -log

Configuring with command line arguments

smtpmock configuration is available as command line arguments specified in the list below:

Flag description	Example of usage
`-host` - host address where smtpmock will run. It's equal to `127.0.0.1` by default	`-host=localhost`
`-port` - server port number. If not specified it will be assigned dynamically	`-port=2525`
`-log` - enables log server activity. Disabled by default	`-log`
`-sessionTimeout` - session timeout in seconds. It's equal to 30 seconds by default	`-sessionTimeout=60`
`-shutdownTimeout` - graceful shutdown timeout in seconds. It's equal to 1 second by default	`-shutdownTimeout=5`
`-failFast` - enables fail fast scenario. Disabled by default	`-failFast`
`-multipleRcptto` - enables multiple `RCPT TO` receiving scenario. Disabled by default	`-multipleRcptto`
`-multipleMessageReceiving` - enables multiple message receiving scenario. Disabled by default	`-multipleMessageReceiving`
`-blacklistedHeloDomains` - blacklisted `HELO` domains, separated by commas	`-blacklistedHeloDomains="example1.com,example2.com"`
`-blacklistedMailfromEmails` - blacklisted `MAIL FROM` emails, separated by commas	`-blacklistedMailfromEmails="a@example1.com,b@example2.com"`
`-blacklistedRcpttoEmails` - blacklisted `RCPT TO` emails, separated by commas	`-blacklistedRcpttoEmails="a@example1.com,b@example2.com"`
`-notRegisteredEmails` - not registered (non-existent) `RCPT TO` emails, separated by commas	`-notRegisteredEmails="a@example1.com,b@example2.com"`
`-responseDelayHelo` - `HELO` response delay in seconds. It's equal to 0 seconds by default	`-responseDelayHelo=2`
`-responseDelayMailfrom` - `MAIL FROM` response delay in seconds. It's equal to 0 seconds by default	`-responseDelayMailfrom=2`
`-responseDelayRcptto` - `RCPT TO` response delay in seconds. It's equal to 0 seconds by default	`-responseDelayRcptto=2`
`-responseDelayData` - `DATA` response delay in seconds. It's equal to 0 seconds by default	`-responseDelayData=2`
`-responseDelayMessage` - Message response delay in seconds. It's equal to 0 seconds by default	`-responseDelayMessage=2`
`-responseDelayRset` - `RSET` response delay in seconds. It's equal to 0 seconds by default	`-responseDelayRset=2`
`-responseDelayQuit` - `QUIT` response delay in seconds. It's equal to 0 seconds by default	`-responseDelayQuit=2`
`-msgSizeLimit` - message body size limit in bytes. It's equal to `10485760` bytes	`-msgSizeLimit=42`
`-msgGreeting` - custom server greeting message	`-msgGreeting="Greeting message"`
`-msgInvalidCmd` - custom invalid command message	`-msgInvalidCmd="Invalid command message"`
`-msgInvalidCmdHeloSequence` - custom invalid command `HELO` sequence message	`-msgInvalidCmdHeloSequence="Invalid command HELO sequence message"`
`-msgInvalidCmdHeloArg` - custom invalid command `HELO` argument message	`-msgInvalidCmdHeloArg="Invalid command HELO argument message"`
`-msgHeloBlacklistedDomain` - custom `HELO` blacklisted domain message	`-msgHeloBlacklistedDomain="Blacklisted domain message"`
`-msgHeloReceived` - custom `HELO` received message	`-msgHeloReceived="HELO received message"`
`-msgInvalidCmdMailfromSequence` - custom invalid command `MAIL FROM` sequence message	`-msgInvalidCmdMailfromSequence="Invalid command MAIL FROM sequence message"`
`-msgInvalidCmdMailfromArg` - custom invalid command `MAIL FROM` argument message	`-msgInvalidCmdMailfromArg="Invalid command MAIL FROM argument message"`
`-msgMailfromBlacklistedEmail` - custom `MAIL FROM` blacklisted email message	`-msgMailfromBlacklistedEmail="Blacklisted email message"`
`-msgMailfromReceived`- custom `MAIL FROM` received message	`-msgMailfromReceived="MAIL FROM received message"`
`-msgInvalidCmdRcpttoSequence` - custom invalid command `RCPT TO` sequence message	`-msgInvalidCmdRcpttoSequence="Invalid command RCPT TO sequence message"`
`-msgInvalidCmdRcpttoArg` - custom invalid command `RCPT TO` argument message	`-msgInvalidCmdRcpttoArg="Invalid command RCPT TO argument message"`
`-msgRcpttoNotRegisteredEmail` - custom `RCPT TO` not registered email message	`-msgRcpttoNotRegisteredEmail="Not registered email message"`
`-msgRcpttoBlacklistedEmail` - custom `RCPT TO` blacklisted email message	`-msgRcpttoBlacklistedEmail="Blacklisted email message"`
`-msgRcpttoReceived` - custom `RCPT TO` received message	`-msgRcpttoReceived="RCPT TO received message"`
`-msgInvalidCmdDataSequence` - custom invalid command `DATA` sequence message	`-msgInvalidCmdDataSequence="Invalid command DATA sequence message"`
`-msgDataReceived` - custom `DATA` received message	`-msgDataReceived="DATA received message"`
`-msgMsgSizeIsTooBig` - custom size is too big message	`-msgMsgSizeIsTooBig="Message size is too big"`
`-msgMsgReceived` - custom received message body message	`-msgMsgReceived="Message has been received"`
`-msgInvalidCmdRsetSequence` - custom invalid command `RSET` sequence message	`-msgInvalidCmdRsetSequence="Invalid command RSET sequence message"`
`-msgInvalidCmdRsetArg` - custom invalid command `RSET` message	`-msgInvalidCmdRsetArg="Invalid command RSET message"`
`-msgRsetReceived` - custom `RSET` received message	`-msgRsetReceived="RSET received message"`
`-msgQuitCmd` - custom quit command message	`-msgQuitCmd="Quit command message"`

Other options

Available not configuration smtpmock options:

Flag description	Example of usage
`-v` - Just prints current `smtpmock` binary build data (version, commit, datetime). Doesn't run the server.	`-v`

Stopping server

smtpmock accepts 3 shutdown signals: SIGINT, SIGQUIT, SIGTERM.

Implemented SMTP commands

id	Command	Sequenceable	Available args	Example of usage
`1`	`HELO`	no	`domain name`, `localhost`, `ip address`, `[ip address]`	`HELO example.com`
`1`	`EHLO`	no	`domain name`, `localhost`, `ip address`, `[ip address]`	`EHLO example.com`
`2`	`MAIL FROM`	can be used after command with id `1` and greater	`email address`, `<email address>`	`MAIL FROM: user@domain.com`
`3`	`RCPT TO`	can be used after command with id `2` and greater	`email address`, `<email address>`	`RCPT TO: user@domain.com`
`4`	`DATA`	can be used after command with id `3`	-	`DATA`
`5`	`RSET`	can be used after command with id `1` and greater	-	`RSET`
`6`	`QUIT`	no	-	`QUIT`

Please note in case when same command used more the one time during same session all saved data upper this command will be erased.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/mocktools/go-smtp-mock. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct. Please check the open tickets. Be sure to follow Contributor Code of Conduct below and our Contributing Guidelines.

License

This golang package is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the smtpmock project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.

Credits

The Contributors for code and awesome suggestions
The Stargazers for showing their support

Versioning

smtpmock uses Semantic Versioning 2.0.0

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README.md

README.md

Table of Contents

Features

Requirements

Installation

Usage

Inside of Golang ecosystem

Configuring

Manipulation with server

Inside of Ruby ecosystem

Example of usage

Inside of any ecosystem

Configuring with command line arguments

Other options

Stopping server

Implemented SMTP commands

Contributing

License

Code of Conduct

Credits

Versioning

Files

README.md

Latest commit

History

README.md

File metadata and controls

Table of Contents

Features

Requirements

Installation

Usage

Inside of Golang ecosystem

Configuring

Manipulation with server

Inside of Ruby ecosystem

Example of usage

Inside of any ecosystem

Configuring with command line arguments

Other options

Stopping server

Implemented SMTP commands

Contributing

License

Code of Conduct

Credits

Versioning