Sending Email using Ruby - SMTP

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 here document, taking care to format the headers correctly. An e-mails requires 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 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 can not 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. Try it once:

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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