[Mimedefang] DoD finally bans HTML e-mail

[David F. Skoll]

WBrown at e1b.org wrote:

> On my original suggestion, would it be worth blocking messages where there 
> is either no plain text or it differs signicantly from the HTML in terms 
> of blocking spam?

Two questions:

1) Should we block messages that contain no text/plain parts?  I would
say no.  There are some people who only send text/html with no corresponding
text/plain.  There are also automated e-mailings that only contain text/html.
So blocking mail for not having a text/plain would lead to false positives.
However, I would strongly suggest blocking mail that lacks a text/* part
entirely.  We've seen some image spams where the top-level MIME type is
image/gif.  It's very hard or impossible to create such messages with most
MUAs; they need to be crafted specially.

2) Should we block messages where the text/html differs "significantly"
from the text/plain?  In theory, yes, but measuring if the difference is
"significant" is nightmarish.  SpamAssassin has some rules that take a stab
at it, but they're not all that good.

Regards,

David.