On Sat, Jan 24, 2004 at 11:50:44AM -0500, Meng Weng Wong wrote:
| On Sat, Jan 24, 2004 at 10:44:24AM -0600, Phil Howard wrote:
| |
| | That said, if SPF goes ahead and treats _only_ NXDOMAIN as the negative
| | response, it's not the end of the world. It will mostly work, but not all
| | DNSBLs can be readily used with "exists".
|
| can you explain? we can add a parameter to exists to handle those.
Some DNSBLs I've seen used some address as a negative, e.g. always returned
an address, but the value of which specified the semantics. I don't recall
which ones were involved. I'm hoping someone recalls the values commonly
used. But there is also the risk that values may not be consistently used.
It may be the case that the blacklists are not using a negative address but
the whitelists are. It was a couple years ago that I looked at the details
of all that. I do know that at the time, Postfix could not handle all of
them correctly.
If you could add an AND/XOR mask option, the returned A record can first be
bitwise-ANDed by the AND mask, then bitwise-XORed by the XOR mask, then the
result can be interpreted as 0.0.0.0 means negative and anything else means
positive (if you didn't know, yet, I program in C). If the AND/XOR mask is
missing, the behaviour would be to AND with 0.0.0.0 and XOR with any non-0
value, to always get positive for any returned A record.
Now, would that need to be an extension of the mechanism, or a modifier.
Doing it at a modifier might be more flexible. But that could also cause
problems if the modifier is unrecognized since it alters the semantics of
the "exists" mechanism (or not, as the case may be), producing inconsistent
results for the same SPF string depending on where the modifier is, or is
not, recognized.
--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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