'Today' considers data retention and IMP

[Florian Weimer]

* Chris Edwards:

> (2) I'm not convinced the certificate check IS dealing with a different
>     risk.  The very people most likely to have the ability to passively 
>     sniff *backbone* links are probably ISP staff, who could just as easily 
>     mount an active attack to defeat opportunistic TLS.  E.g redirect SMTP
>     to a transparent proxy, effectively man-in-the-middle'ing the TLS.

It has already happened that some on-path device filtered out the
STARTTLS capability in the EHLO response, leading to transmission in
the clear:

  <http://www.heise.de/security/news/meldung/116073>

The ISP claimed that this was purely by accident, which is quite
plausible (unfortunately).