a dot alone in a line (bug?)

[bogo at escom.com]

Yes, it is a bug if a sending MTA sends a message with such a dot 
embedded in the message itself.  But then the problem would be 
with the sending MTA.

The "dot on a line by itself" is an RFC standard rather than
just a mechanism used by sendmail.  See Example 1 of RFC 821,
which shows a <CR><LF>.<CR><LF> sequence as the end of message.
The first CRLF is usually generated at the end of the previous (last)
line, and so the dot indeed begins on a line by itself.

I don't believe Postel defines this as an out-of-band signal,
but that's the intent.  So if a sending MTA sends one in the
middle of a message, then the sending MTA is broken. 
If a user submits this to a sending MTA, then the sending MTA
can convert it a double dot sequence, append a space, or just 
teach the sending user an important lesson about SMTP. :-)
If a broken zombie forwarder spews a bunch of data with a
dot in the middle of the data, then the receiving MTA should
ignore everything after that dot.  (Actually, it should ignore
the zombie, but that's a different thread.) If a receiving MTA 
records one, and tries to forward it, then the receiving MTA is broken.

Different implementations may record the dot at the end of message 
and strip it later on.  I think that's what Matthias is suggesting 
when he asks for the the code used to interface bogofilter to 
other mail software.

I don't know what assumptions bogofilter makes or what it does
when it sees such a dot, but if bogofilter terminates scanning
and returns the result up to that point, then I would argue that
bogofilter is doing the best it can with bad data.

Al Donaldson