Thursday May 04, 2006

Email sent from Mac OS Mail and read by other mail clients appears to have extra spaces inserted throughout the message, including spaces that break some URLs into two pieces, rendering them invalid and unclickable.

Apple's crime as it were is that they've apparently adopted a relatively new email standard which has not yet been implemented in many (any?) other common mail clients like Mozilla Mail, Thunderbird, or Outlook. That would be okay if they'd made the feature optional, but there doesn't seem to be a way to turn it off. And, worse, their implementation of the new feature is wrong...or at least poorly done. They shouldn't be segmenting URLs.

The new feature is the DelSp parameter that is described in RFC-3676. It is used to implement a new way of inserting soft breaks into Text/Plain email that is meant to be flowed (Format=Flowed), the default for Mac OS plain text email when any lines in the message exceed 72 characters. Soft breaks are marked by ending a line with a space, followed by a line break. The message header specifies "DelSp=yes", which instructs the receiving mailer to logically delete the ending space and the line break. If a URL was broken apart in this way by the sending mailer, the receiving mailer will reconstruct it by removing the intervening space and the line break. Unless, of course, the receiving mailer doesn't recognize the DelSp parameter, in which case URLs will be split by intervening space and won't be valid, clickable links.

I said that Apple's implementation is wrong or at least poorly done because the RFC states the following:

Regardless of which technique is used, a generating agent SHOULD NOT insert a space in an unnatural location, such as into a word (a sequence of printable characters, not containing spaces, in a language/coded character set in which spaces are common). If faced with such a word which exceeds 78 characters (but less than 998 characters, the [SMTP] limit on line length), the agent SHOULD send the word as is and exceed the 78-character limit on line length.

While it's true that the language says SHOULD and not MUST, breaking URLs is really poor form. Apple should fix this problem.