Mutt: Show HTML for sites that send broken HTML mail (Shallow Thoughts)

Akkana's Musings on Open Source Computing, Science, and Nature.

Mon, 29 Jul 2013

Mutt: Show HTML for sites that send broken HTML mail

Increasingly I'm seeing broken sites that send automated HTML mail with headers claiming it's plain text.

To understand what's happening, you have to know about something called MIME multipart/alternative.

MIME stands for Multipurpose Internet Mail Extensions: it's the way mail encodes different types of attachments, so you can attach images, music, PDF documents or whatever with your email.

If you send a normal plain text mail message, you don't need MIME. But as soon as you send anything else -- like an HTML message where you've made a word bold, changed color or inserted images -- you need it. MIME adds a Content-Type to the message saying "This is HTML mail, so you need to display it as HTML when you receive it" or "Here's a PDF attachment, so you need to display it in a PDF viewer". The headers for these two cases would look like this:

Content-Type: text/html
Content-Type: application/pdf

A lot of mail programs, for reasons that have never been particularly clear, like to send two copies of every mail message: one in plain text, one in HTML. They're two copies of the same message -- it's just that one version has fancier formatting than the other. The MIME header that announces this is

Content-Type: multipart/alternative
because the two versions, text and HTML, are alternative versions of the same message. The recipient need only read one, not both. Inside the multipart/alternative section there will be further MIME headers, one saying Content-Type: text/plain, where it puts the text of your message, and one Content-Type: text/html, where it puts HTML source code.

This mostly works fine for real mail programs (though it's a rather silly waste of bandwidth, sending double copies of everything for no particularly good reason, and personally I always configure the mailers I use to send only one copy at a time). But increasingly I'm seeing automated mail robots that send multipart/alternative mail, but do it wrong: they send HTML for both parts, or they send a valid HTML part and a blank text part.

Why don't the site owners notice the problem?

You wouldn't ever notice a problem if you use the default configuration on most mailers, to show the HTML part if at all possible. But most mail programs give you an option to show the text part if there is one. That way, you don't have to worry about those people who like to send messages in pink blinking text on a plaid background -- all you see is the text.

If your mailer is configured to show plain text, for most messages you'll see just text -- no colors, no blinking, no annoyances. But for mail sent by these misconfigured mail robots, what you'll see is HTML source code.

I've seen this in several places -- lots of spammers do it (who cares? I was going to delete the message anyway), and one of the local astronomy clubs does it so I've long since stopped trying to read their announcements. But the latest place I've seen this is one that ought to know better: Coursera. They apparently reconfigured their notification system recently, and I started getting course notifications that look like this:

/* Client-specific Styles */
#outlook a{padding:0;} /* Force Outlook to provide a "view in browser" button.
*/
body{width:100% !important;} .ReadMsgBody{width:100%;}
.ExternalClass{width:100%;} /* Force Hotmail to display emails at full width */
body{-webkit-text-size-adjust:none;} /* Prevent Webkit platforms from changing
default text sizes. */
/* Reset Styles */
body{margin:0; padding:0;}
img{border:0; height:auto; line-height:100%; outline:none;
text-decoration:none;}
table td{border-collapse:collapse;}
#backgroundTable{height:100% !important; margin:0; padding:0; width:100%
!important;}
p {margin-top: 14px; margin-bottom: 14px;}
/* /\/\/\/\/\/\/\/\/\/\ STANDARD STYLING: PREHEADER /\/\/\/\/\/\/\/\/\/\ */
.preheaderContent div a:link, .preheaderContent div a:visited, /* Yahoo! Mail
Override */ .preheaderContent div a .yshortcuts /* Yahoo! Mail Override */{
  color: #3b6e8f;
... and on and on like that. You get the idea. It's unreadable, even by a geek who knows HTML pretty well. It would be fine in the HTML part of the message -- but this is what they're sending in the text/plain part.

I filed a bug, but Coursera doesn't have a lot of staff to respond to bug reports and it might be quite some time before they fix this. Meanwhile, I don't want to miss notifications for the algorithms course I'm currently taking. So I needed a workaround.

How to work around the problem in mutt

I found one for mutt at alternative_order and folder-hook. When in my "classes" folder, I use a folder hook to tell mutt to prefer text/html format over text/plain, even though my default is text/plain. Then you also need to add a default folder hook to set the default back for every other folder -- mutt folder hooks are frustrating in that way.

The two folder hooks look like this:

folder-hook . 'set unalternative_order *; alternative_order text/plain text'

# Prefer the HTML part but only for Coursera,
# since it sends HTML in the text part.
folder-hook =in/coursera 'unalternative_order *; alternative_order text/html'

alternative_order specifies which types you'd most like to read. unalternative_order is a lot less clear; the documentation says it "removes a mime type from the alternative_order list", but doesn't say anything more than that. What's the syntax? What's the difference between using unalternative_order or just re-setting alternative_order? Why do I have to specify it with * in both places? No one seems to know.

So it's a little unsatisfying, and perhaps not the cleanest way. But it does work around the bug for sites where you really need a way to read the mail.

Update: I also found this discussion of alternative_order which gives a nice set of key bindings to toggle interactively between the various formats. It was missing some backslashes, so I had to fiddle with it slightly to get it to work. Put this in .muttrc:

macro pager ,@aoh= "\
<enter-command> unalternative_order *; \
alternative_order text/enriched text/html text/plain text;\
macro pager A ,@aot= 'toggle alternative order'<enter>\
<exit><display-message>"

macro pager ,@aot= "\
<enter-command> unalternative_order *; \
alternative_order text/enriched text/plain text/html text;\
macro pager A ,@aoh= 'toggle alternative order'<enter>\
<exit><display-message>"

macro pager A ,@aot= "toggle alternative order"

Then just type A (capital A) to toggle between formats. If it doesn't change the first time you type A, type another one and it should redisplay. I've found it quite handy.

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[ 15:13 Jul 29, 2013    More tech/email | permalink to this entry | comments ]
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