Newlines resolved as =0A in Sendgrid X-SMTPAPI header

Question

I am using Sendgrid to send email to a mailing list, using the X-SMTPAPI header to specify the multiple recipients. From the Sendgrid documentation "Headers must be wrapped to keep the line length under 72."

I am using the ActionMailer to send emails, and setting the X-SMTPAPI header using the headers method. To keep lines less than 72 characters, I have tried replacing each comma with a comma+newline+space. For example,

headers["X-SMTPAPI"] = {
        :to => ['user1@example.com','user2@example.com','user3@example.com','user4@example.com','user5@example.com','user6@example.com']
}.to_json.gsub(',',",\n ")

Instead of getting newlines in my header, I am getting the following (from the log file)

X-SMTPAPI: {"to":["user1@example.com",=0A "user2@example.com",=0A "user3@example.com",=0A "user4@example.com",=0A "user5@example.com",=0A "user6@example.com"]}

Note that the \n characters are being replaced with =0A. This sequence is rejected as invalid by the Sendgrid server.

Any ideas what I can do to get the proper newlines into the header?

Edit: I tried adding a "puts headers" to see what is being set in the headers. Then is what I found

Date: Sat, 13 Apr 2013 18:21:36 -0400
Message-ID: <5169da701cd26_5343fe1776afc50749b4@saunders.mail>
Mime-Version: 1.0
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
X-SMTPAPI: {"to":["user1@example.com",=0A "user2@example.com",=0A
 "user3@example.com",=0A "user4@example.com",=0A "user5@example.com",=0A
 "user6@example.com"]}

Note the newlines I am adding are still showing up as "=0A". But something appears to be adding wrapping on its own. Is this wrapping automatic, and sufficient to keep my header line length from exceeding the requirements?

Answer 1

ActionMailer actually will handle folding and encoding the lines for you if you give it the proper spacing to do so. You should use JSON.generate to give it the spacing:

Ex.

headers["X-SMTPAPI"] = JSON.generate({
  :category => "welcome_email",
  :to => ['user1@example.com','user2@example.com','user3@example.com','user4@example.com','user5@example.com','user6@example.com']
}, :indent => ' ')

Which would result in:

X-SMTPAPI: { "category":"welcome_email", "to":[  "user1@example.com",
 "user2@example.com",  "user3@example.com",  "user4@example.com",  
 "user5@example.com",     "user6@example.com"]}

As you can see, when ActionMailer encounters whitespace, it will wrap things for you - no need for the usual \r\n.

Answer 2

It seems like characters in headers have to be encoded according to the rules of RFC 2047 [14].
Accodingly to ASCII table %0A states for \n