Thanks for all the responses. Here's a recap of what I think I heard...
RFC822 [and possibly RFC2822 when I can find a copy since it's not on the ietf
web site, where does one get a copy?] allows single NL characters in header
field bodies, which are supposed to be treated as normal characters, distinct
from the CR-NL pair that indicates the end of a line. The receiving
transformation will probably preserve these, but the result on a *N[IU]X system
is likely to be an illegal header since the NL will start another line which
is not likely to be a valid header field. Hey, this could be a great spam hack;
put a NL in, for example, the subject field, followed by a legal looking but
completely bogus received field.
RFC822 allows NUL character in header field bodies. This probably will break
most *N[IU]X mail programs.
Neither of these are problems at the moment because nobody is doing this stuff.
But if, for example, Microsoft decided to being every mail header field name
with a NUL it would be legal while breaking lots of things.
Is this a correct recap?
Jon Steinhart
