On Wed, 27 Apr 2011 08:33:18 +0200, Ingo Molnar said:
> Also, sendmail does not screw up From: headers that are in the body of the 
> email - forwarding emails is one of the oldest things that can be done to 
> emails.

What some Sendmail configurations *do* eat is lines that start with 'From ' (no
colon). Those will get escaped as '>From ...'  to prevent them from looking
like a separator line for what's known as 'mbox' format - which is basically
the same info as in the Return-Path: header plus a timestamp. They look like:

>From hostmaster@prairie.net Fri Apr 19 15:50:15 2002

(If the above line has a >From, you have the issue.  Yes, it could be smarter
and do a full parse for a mbox header rather than just '^From '.  And yes, I
had to go digging to find an old archived mbox format file to snarf the example
from.