421 4.3.0 deliver: Trying to unput wrong character

[Joseph Brennan]

> This is one of those weird inconsistencies between IMAP and SMTP protocols …
> as far as I remember, the NUL character restriction only applies to the IMAP
> protocol … so your MTA (e.g. sendmail) is not breaking the SMTP RFC by
> transferring them.

True, but it's breaking the Internet Message Format RFC, namely RFC
2822. Under "Obsolete Syntax" includes this:

   Finally, certain characters that were formerly allowed in messages
   appear in this section.  The NUL character (ASCII value 0) was once
   allowed, but is no longer for compatibility reasons.

Compatibility with POP and IMAP, presumably.

Sendmail seems to be following still the old "be generous in what you
accept" maxim, and as a result it accepts something that modern
software cannot read-- just in case you have some odd way of reading
mail that can handle it.


-- 
Joseph Brennan
Columbia University