Email subject not correctly assigned with Ruby net/smtp

Question

I use Ruby net/smtp

require 'net/smtp'

I send mails using the following method:

Net::SMTP.start(SMTP_SERVER) do |smtp|
  smtp.send_message(message,"mailman-ruby@example.de",reciepent)
end

I want to add a subject to the mails i send but couldn't find one in the documentation.

What I tried so far is putting the subject into the message like this:

<<END_OF_MESSAGE
Subject: test message
. . . rest of the message
END_OF_MESSAGE

Unfortunally that doesnt do the trick!

Anyone knows how to set subject using 'smtp/net'?

Answer 1

net/smtp is a very low-level library. It expects the message to be an email message, including all the headers.

From the documentation

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

In your case, make sure to add a new line between the Headers and the body. Change

<<END_OF_MESSAGE
Subject: test message
. . . rest of the message
END_OF_MESSAGE

to

<<END_OF_MESSAGE
Subject: test message
. . . rest of the message
END_OF_MESSAGE

Instead of using net/smtp, I highly encourage you to use mail. mail uses a more high level interface for sending email messages without loosing the control of the message.

If you don't really care about advanced usage, you can also switch to pony.

Answer 2

The responsibility of the subject is not that of the SMTP protocol. It is held in one of the SMTP commands, which is to say DATA and as such, is not relevant in responsibility to that library.

However, the DATA will contain either proper (specification indicated) headers, or even some headers that are not specified, but not disallowed. PGP

According to RFC 5321 (and as expected) "Server SMTP systems SHOULD NOT reject messages based on perceived defects in the RFC 822 or MIME (RFC 2045 [21]) message header section or message body.".

So, your answer is going to be: "You don't set the subject by using that." But you would set the DATA with that information in it.

And the documentation that you linked to has an example of doing exactly that:

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

Documentation not linked here, as you have already provided the link.