Daniel Taylor wrote:
For domains that cannot publish TXT records:
Publish one of the following as a CNAME record for the domain:
spfdefault-weak
spfdefault-soft
spfdefault-strict
These would indicate the desire but inability to publish
a proper SPF record.
spfdefault-weak would indicate "v=spf1 a mx ?all"
spfdefault-soft would indicate "v=spf1 a mx ~all"
spfdefault-strict would indicate "v=spf1 a mx -all"
I exclude PTR records from this as I assume that if you
can't publish TXT you are unlikely to have authoritative PTR
capability as well.
Admittedly this only doubles the load on an SPF-checker, but once you
multiply the proportion of all domain users that can create CNAME but
not TXT (unknown, but pretty small - I'll be very generous and estimate
5%) by the proportion of users that use one of the above records (5% of
those known by spf.infinitepenguins.net), you have an expected usage of
about 1 in 400 spf-publishing domains (say 1 in 4000 of all domains if
SPF takeup increases by a factor of 10).
Don't think it's worth, it really.
Wechsler