Question

Alright. I thought this problem had something to do with my rails app, but it seems to have to do with the deeper workings of email attachments.

I have to send out a csv file from my rails app to a warehouse that fulfills orders places in my store. The warehouse has a format for the CSV, and ironically the header line of the CSV file is super long (1000+ characters).

I was getting a line break in the header line of the csv file when I received the test emails and couldn’t figure out what put it there. However, some googling has finally showed the reason: attached files have a line character limit of 1000. Why? I don’t know. It seems ridiculous, but I still have to send this csv file somehow.

I tried manually setting the MIME type of the attachment to text/csv, but that was no help. Does anybody know how to solve this problem?

Some relevant google results : http://www.google.com/search?client=safari&rls=en&q=csv+wrapped+990&ie=UTF-8&oe=UTF-8

update

I’ve tried encoding the attachment in base64 like so:

    attachments['205.csv'] = {:data=> ActiveSupport::Base64.encode64(@string), :encoding => 'base64', :mime_type => 'text/csv'}

That doesn’t seem to have made a difference. I’m receiving the email with a me.com account via Sparrow for Mac. I’ll try using gmail’s web interface.

Answer 1

This seems to be because the SendGrid mail server is modifying the attachment content. If you send an attachment with a plain text storage mime type (e.g text/csv) it will wrap the content every 990 characters, as you observed. I think this is related to RFC 2045/821:

6. Content-Transfer-Encoding Header Field

   Many media types which could be usefully transported via email are
   represented, in their "natural" format, as 8bit character or binary
   data. Such data cannot be transmitted over some transfer protocols.
   For example, RFC 821 (SMTP) restricts mail messages to 7bit US-ASCII
   data with lines no longer than 1000 characters including any trailing
   CRLF line separator.

   It is necessary, therefore, to define a standard mechanism for
   encoding such data into a 7bit short line format. Proper labelling
   of unencoded material in less restrictive formats for direct use over
   less restrictive transports is also desireable. This document
   specifies that such encodings will be indicated by a new "Content-
   Transfer-Encoding" header field. This field has not been defined by
   any previous standard.

If you send the attachment using base64 encoding instead of the default 7-bit the attachment remains unchanged (no added line breaks):

attachments['file.csv']= { :data=> ActiveSupport::Base64.encode64(@string), :encoding => 'base64' }