Re: DMARC: perspectives from a listadmin of large open-source lists

["John R Levine" <[e-mail]>]

> Sadly, there are a non-trivial number of MTA installations whose
> implementers or operators, having discovered that they had not
> seen a legitimate use of the percent hack in years, decided that
> they were about as likely to appear in legitimate messages as
> source routing and dealt with them accordingly.  Put more
> simply, a "%" in a local-part may be least as likely to get a
> message rejected or dumped as a badly specified DMARC record, so
> the one is really not a very good cure for the other.

Since the percent hack became a famous vector for open relay abuse, so we 
all stopped honoring it.  A lot of MTAs still reject anything with a % 
saying something like no more source routing.  Mine does.

So this would require inventing something with the same semantics as the 
percent hack, but a different syntax.  Perhaps we can use an exclamation 
point.

Regards,
John Levine, ima![e-mail]
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