[Mimedefang] Want to modify "read-receipt" img tags in mail

[David F. Skoll]

On Thu, 20 May 2004, Paul Murphy wrote:

> C.  Occasionally, someone will use HTML mail with a "stationery"
> effect, which is normally an image tiled across the background, or a
> logo Detect that the image is in the background, and ignore it.

How?

Are you proposing doing CSS parsing on the mail server?  That's the only
reliable way to detect "stationery".

HTML mail is evil.  HTML plus Javascript mail is pure evil.  HTML
plus Javascript plus CSS mail is pure, unadulterated evil.

> D.  Self-referential e-mail, with images attached and referenced in the HTML
> 	Links to attached images are OK, so ignore it.

Some spams come in that way (a couple a year for us.)

> You could in theory parse all HTML parts of messages, and identify
> every off-site link.

No; too many problems (as you noted.)

> The alternative is much simpler - if the HTML contains any URI which
> is off-site, then change the message to be a plain-text body with
> the original message as an attachment.  In the plain text part,
> provide a list of the sites referenced, and a warning that the
> off-site links could be used for tracking.  Implement a whitelist
> system for this, so messages from approved sites, or to users who
> elect to opt out of the filtering, are passed unchanged.

That's not a bad idea, but in my experience, people (a) complain like
crazy and (b) get very nervous when they see an "attachment".

> The other option, much as I hate to say it, is to try a smarter mail client,
> such as Outlook 2003,

Feh.  Try Pine. :-)

Regards,

David.