Programming language: Crystal
License: MIT License
Tags: Email    

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EMail for Crystal

Build Status

Simple email sending library for the Crystal programming language.

You can:

  • construct an email with a plain text message, a HTML message and/or some attachment files.
  • include resources(e.g. images) used in the HTML message.
  • set multiple recipients to the email.
  • use multibyte characters(only UTF-8) in the email.
  • send the email by using local or remote SMTP server.
  • use TLS connection by SMTP orver SSL/TLS(new) or STARTTLS command.
  • use SMTP-AUTH by AUTH PLAIN or AUTH LOGIN when using TLS.
  • send multiple emails concurrently by using multiple smtp connections.

You can not:

  • use ESMTP features except those mentioned above.


First, add the dependency to your shard.yml:

    github: arcage/crystal-email

Then, run shards install


To send a minimal email message:

require "email"

# Create email message
email = EMail::Message.new
email.from    "[email protected]"
email.to      "[email protected]"
email.subject "Subject of the mail"
email.message <<-EOM
  Message body of the mail.

  Your Signature

# Set SMTP client configuration
config = EMail::Client::Config.new("your.mx.example.com", 25)

# Create SMTP client object
client = EMail::Client.new(config)

client.start do
  # In this block, default receiver is client

This code will output log entries to STDOUT as follows:

2018/01/25 20:35:09 [e_mail.client/12347] INFO [EMail_Client] Start TCP session to your.mx.example.com:25
2018/01/25 20:35:10 [e_mail.client/12347] INFO [EMail_Client] Successfully sent a message from <[email protected]> to 1 recipient(s)
2018/01/25 20:35:10 [e_mail.client/12347] INFO [EMail_Client] Close TCP session to your.mx.example.com:25

Client configs

You can set some connection settings to EMail::Client::Config object.

That can make SMTP connection to use TLS / SMTP AUTH, or output more detailed log message.

See EMail::Client::Config for more details.

Email message

You can set more email headers to EMail::Message object.

And, you can also send emails including attachment files, HTML message, and/or resource files related message body(e.g. image file for HTML message).

See EMail::Message for more details.

Concurrent sending

Note: this feature supports the concurrent(not parallel) sending with only one thread.

By using EMail::ConcurrentSender object, you can concurrently send multiple messages by multiple connections.

rcpt_list = ["[email protected]", "[email protected]", "[email protected]", "[email protected]"]

# Set SMTP client configuration
config = EMail::Client::Config.new("your.mx.example.com", 25)

# Create concurrent sender object
sender = EMail::ConcurrentSender.new(config)

# Sending emails with concurrently 3 connections.
sender.number_of_connections = 3

# Sending max 10 emails by 1 connection.
sender.messages_per_connection = 10

# Start email sending.
sender.start do
  # In this block, default receiver is sender
  rcpts_list.each do |rcpt_to|
    # Create email message
    mail = EMail::Message.new
    mail.from "[email protected]"
    mail.to rcpt_to
    mail.subject "Concurrent email sending"
    mail.message "message to #{rcpt_to}"
    # Enqueue the email to sender
    enqueue mail

See EMail::ConcurrentSender for more details.


The v0.34.0 of Crystal language has drastic changes in the logging functions. To fit it, the v0.5.0 of this shard also changes the logging behaviour.

You can use two kinds of logger(Log type object), the default logger and the client specific logger.

The default logger is declered on the EMail::Client type. It can be got by EMail::Client.log, and change its behavior by EMail::Client.log_***= methods.

On the other hand, the client specific logger will be set to EMail::Client instance itself by EMail::Client::Config setting. With this, you can use your own logger for the EMail::Client object.

If the EMail::Client object has the client specific logger, the client use it to output the log entries. Otherwise, the client use the default logger.

See EMail::Client and EMail::Client::Config for more details.

Debug log

When you set the log level to Log::Severity::Debug, you can see all of the SMTP commands and the resposes in the log entries.

EMail::Client.log_level = Log::Severity::Debug

Debug log are very useful to check how SMTP session works.

But, in the case of using SMTP AUTH, the debug log includes Base64 encoded user ID and passowrd. You should remenber that anyone can decode the authentication information from the debug log. And, you should use that very carefully.


  • arcage ʕ·ᴥ·ʔAKJ - creator, maintainer


Thank you for valuable contributions.