--On Dienstag, Februar 24, 2004 15:51:12 -0600 wayne <wayne(_at_)midwestcs(_dot_)com>
wrote:
[...]
On a somewhat related subject, it would be nice if you could mark SPF
records as being valid for include: mechanisms only. It is awfully
tempting to use something like include:%{l}.spf.%{d}, and have that
resolve to "v=spf1 +all" in some cases. However, that opens up those
subdomains for being abused.
Just use an underscore as part of the subdomain. There can be no valid
hostnames with this subdomain and thus any attempt to abuse it by faking
mail addresses in this subdomain will fail even the most superficial
syntactic check.
Ralf