Sending Email using Ruby - SMTP

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Simple Mail Transfer Protocol (SMTP) is a protocol, which handles sending e-mail and routing e-mail between mail servers.

Ruby provides Net::SMTP class for Simple Mail Transfer Protocol (SMTP) client-side connection and provides two class methods new and start.

  • The new takes two parameters −

    • The server name defaulting to localhost.

    • The port number defaulting to the well-known port 25.

  • The start method takes these parameters −

    • The server − IP name of the SMTP server, defaulting to localhost.

    • The port − Port number, defaulting to 25.

    • The domain − Domain of the mail sender, defaulting to ENV["HOSTNAME"].

    • The account − Username, default is nil.

    • The password − User password, defaulting to nil.

    • The authtype − Authorization type, defaulting to cram_md5.

An SMTP object has an instance method called sendmail, which will typically be used to do the work of mailing a message. It takes three parameters −

  • The source − A string or array or anything with an each iterator returning one string at a time.

  • The sender − A string that will appear in the from field of the email.

  • The recipients − A string or an array of strings representing the recipients' addressee(s).

Example

Here is a simple way to send one email using Ruby script. Try it once −

require 'net/smtp'

message = <<MESSAGE_END
From: Private Person <me@fromdomain.com>
To: A Test User <test@todomain.com>
Subject: SMTP e-mail test

This is a test e-mail message.
MESSAGE_END

Net::SMTP.start('localhost') do |smtp|
  smtp.send_message message, 'me@fromdomain.com', 'test@todomain.com'
end

Here, you have placed a basic e-mail in message, using a document, taking care to format the headers correctly. E-mails require a From, To, and Subject header, separated from the body of the e-mail with a blank line.

To send the mail you use Net::SMTP to connect to the SMTP server on the local machine and then use the send_message method along with the message, the from address, and the destination address as parameters (even though the from and to addresses are within the e-mail itself, these aren't always used to route mail).

If you're not running an SMTP server on your machine, you can use the Net::SMTP to communicate with a remote SMTP server. Unless you're using a webmail service (such as Hotmail or Yahoo! Mail), your e-mail provider will have provided you with outgoing mail server details that you can supply to Net::SMTP, as follows −

Net::SMTP.start('mail.your-domain.com')

This line of code connects to the SMTP server on port 25 of mail.your-domain.com without using any username or password. If you need to, though, you can specify port number and other details. For example −

Net::SMTP.start('mail.your-domain.com', 
                25, 
                'localhost', 
                'username', 'password' :plain)

This example connects to the SMTP server at mail.your-domain.com using a username and password in plain text format. It identifies the client's hostname as localhost.

Sending an HTML e-mail using Ruby

When you send a text message using Ruby then all the content will be treated as simple text. Even if you will include HTML tags in a text message, it will be displayed as simple text and HTML tags will not be formatted according to HTML syntax. But Ruby Net::SMTP provides option to send an HTML message as actual HTML message.

While sending an email message you can specify a Mime version, content type and character set to send an HTML email.

Example

Following is the example to send HTML content as an email. Try it once −

require 'net/smtp'

message = <<MESSAGE_END
From: Private Person <me@fromdomain.com>
To: A Test User <test@todomain.com>
MIME-Version: 1.0
Content-type: text/html
Subject: SMTP e-mail test

This is an e-mail message to be sent in HTML format

<b>This is HTML message.</b>
<h1>This is headline.</h1>
MESSAGE_END

Net::SMTP.start('localhost') do |smtp|
   smtp.send_message message, 'me@fromdomain.com', 'test@todomain.com'
end

Sending Attachments as an e-mail

To send an email with mixed content requires to set Content-type header to multipart/mixed. Then text and attachment sections can be specified within boundaries.

A boundary is started with two hyphens followed by a unique number, which cannot appear in the message part of the email. A final boundary denoting the email's final section must also end with two hyphens.

Attached files should be encoded with the pack("m") function to have base64 encoding before transmission.

Example

Following is the example, which will send a file /tmp/test.txt as an attachment.

require 'net/smtp'

filename = "/tmp/test.txt"
# Read a file and encode it into base64 format
filecontent = File.read(filename)
encodedcontent = [filecontent].pack("m")   # base64

marker = "AUNIQUEMARKER"
body = <<EOF
This is a test email to send an attachement.
EOF

# Define the main headers.
part1 = <<EOF
From: Private Person <me@fromdomain.net>
To: A Test User <test@todmain.com>
Subject: Sending Attachement
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary = #{marker}
--#{marker}
EOF

# Define the message action
part2 = <<EOF
Content-Type: text/plain
Content-Transfer-Encoding:8bit

#{body}
--#{marker}
EOF

# Define the attachment section
part3 = <<EOF
Content-Type: multipart/mixed; name = \"#{filename}\"
Content-Transfer-Encoding:base64
Content-Disposition: attachment; filename = "#{filename}"

#{encodedcontent}
--#{marker}--
EOF

mailtext = part1 + part2 + part3

# Let's put our code in safe area
begin 
   Net::SMTP.start('localhost') do |smtp|
      smtp.sendmail(mailtext, 'me@fromdomain.net', ['test@todmain.com'])
   end
rescue Exception => e  
   print "Exception occured: " + e  
end

NOTE − You can specify multiple destinations inside the array but they should be separated by comma.

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