Hi Andriy,
I am a bit late coming to this thread but here is my opinion on it.
A prefix is useful if you want to differentiate between the TXT record at
the domain itself, and the TXT record that is specific to SPF. This
presumes that domains already have TXT records for some other usage, and
that other usage is more important than SPF, and presumes that there will
be a conflict due to size or content.
I have not found any of these factors to exist with the domains I have
worked with. Most domains don't have TXT in them at all, and not at the
top level, and for those that do, adding another TXT at the top level will
not make the TXT response too big, so they can safely coexist.
Here is another point to consider... if SPF had its own RR type, we
wouldn't need to worry about prefixes, right? You normally don't apply a
prefix for MX, like "mx.mydomain.com", you just say "dig mydomain.com MX".
This is how DNS normally works, and I think it's better to just use TXT in
the same way, to avoid confusing the users. (Eventually if we get our own
RR type this will be probably be the way it is used, just like we use MX
today)
Anyway, I think that's why it is set up the way it is now. I can see your
point, and there are valid reasons on both sides, not really right or
wrong, I just think it's easier for admins to understand and implement this
way.
gregc
--
Greg Connor <gconnor(_at_)nekodojo(_dot_)org>