class Net::SMTP

What is This Library?

This library provides functionality to send internet mail via SMTP, the Simple Mail Transfer Protocol. For details of SMTP itself, see [RFC5321]. This library also implements SMTP authentication, which is often necessary for message composers to submit messages to their outgoing SMTP server, see [RFC6409], and [SMTPUTF8], which is necessary to send messages to/from addresses containing characters outside the ASCII range.

What is This Library NOT?

This library does NOT provide functions to compose internet mails. You must create them by yourself. If you want better mail support, try the mail or rmail gems, or search for alternatives in RubyGems.org or The Ruby Toolbox.

FYI: the official specification on internet mail is: [RFC5322].

Examples

Sending Messages

You must open a connection to an SMTP server before sending messages. The first argument is the address of your SMTP server, and the second argument is the port number. Using SMTP.start with a block is the simplest way to do this. This way, the SMTP connection is closed automatically after the block is executed.

require 'net/smtp'
Net::SMTP.start('your.smtp.server', 25) do |smtp|
  # Use the SMTP object smtp only in this block.
end

Replace ‘your.smtp.server’ with your SMTP server. Normally your system manager or internet provider supplies a server for you.

Then you can send messages.

msgstr = <<END_OF_MESSAGE
From: Your Name <your@mail.address>
To: Destination Address <someone@example.com>
Subject: test message
Date: Sat, 23 Jun 2001 16:26:43 +0900
Message-Id: <unique.message.id.string@example.com>

This is a test message.
END_OF_MESSAGE

require 'net/smtp'
Net::SMTP.start('your.smtp.server', 25) do |smtp|
  smtp.send_message msgstr,
                    'your@mail.address',
                    'his_address@example.com'
end

Closing the Session

You MUST close the SMTP session after sending messages, by calling the finish method:

# using SMTP#finish
smtp = Net::SMTP.start('your.smtp.server', 25)
smtp.send_message msgstr, 'from@address', 'to@address'
smtp.finish

You can also use the block form of SMTP.start or SMTP#start. This closes the SMTP session automatically:

# using block form of SMTP.start
Net::SMTP.start('your.smtp.server', 25) do |smtp|
  smtp.send_message msgstr, 'from@address', 'to@address'
end

I strongly recommend this scheme. This form is simpler and more robust.

HELO domain

In almost all situations, you must provide a third argument to SMTP.start or SMTP#start. This is the domain name which you are on (the host to send mail from). It is called the “HELO domain”. The SMTP server will judge whether it should send or reject the SMTP session by inspecting the HELO domain.

Net::SMTP.start('your.smtp.server', 25, helo: 'mail.from.domain') do |smtp|
  smtp.send_message msgstr, 'from@address', 'to@address'
end

SMTP Authentication

The Net::SMTP class supports the SMTP extension for SASL Authentication

RFC4954

and the following

SASL mechanisms: PLAIN, LOGIN _(deprecated)_, and CRAM-MD5 _(deprecated)_.

To use SMTP authentication, pass extra arguments to SMTP.start or SMTP#start.

# PLAIN
Net::SMTP.start('your.smtp.server', 25,
                user: 'Your Account', secret: 'Your Password', authtype: :plain)

Support for other SASL mechanisms-such as EXTERNAL, OAUTHBEARER, SCRAM-SHA-256, and XOAUTH2-will be added in a future release.

The LOGIN and CRAM-MD5 mechanisms are still available for backwards compatibility, but are deprecated and should be avoided.