tlug: MTA's that change "From" to ">From" in mail messages

["Stephen J. Turnbull" <turnbull@example.com>]

>>>>> "Selva" == Selva Nair <selva@example.com> writes:

    Selva> So the question is, what do the standards say? RFC 821 does
    Selva> not appear to mention anything of that kind, while what I
    Selva> could glean from RFC1521 appears to indicate that
    Selva> conforming MTA's are not supposed to do that...

I'm not sure what 821 (and 1123) say about this, or if they apply (I
suspect that here (modern) sendmail is acting as a Mail Delivery Agent
rather than a MTA, and that it doesn't do any such thing as an MTA),
but RFC 1521 is seriously obsolete (AFAIK RFCs 2054-2049 are mostly
current).  RFC 2049 says (pp. 7-8)

    (8)   Some mail transport agents will corrupt data that
          includes certain literal strings.  In particular, a
          period (".") alone on a line is known to be corrupted
          by some (incorrect) SMTP implementations, and a line
          that starts with the five characters "From " (the fifth
          character is a SPACE) are commonly corrupted as well.
          A careful composition agent can prevent these
          corruptions by encoding the data (e.g., in the quoted-
          printable encoding using "=46rom " in place of "From "
          at the start of a line, and "=2E" in place of "." alone
          on a line).

   Please note that the above list is NOT a list of recommended
   practices for MTAs.  RFC 821 MTAs are prohibited from altering the
   character of white space or wrapping long lines.  These BAD and
   invalid practices are known to occur on established networks, and
   implementations should be robust in dealing with the bad effects they
   can cause.

I believe that Smail provides a way to prevent the >From hack from
being used (although I couldn't find in the docs).

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