On Friday 21 November 2003 2:20 pm, Marc wrote:
Let's assume group (2) can handle anything we throw at them.
All I'm saying is that I believe that there are a LOT of people that fit
into this category.
If you do not have TXT record capability but do have a web server mapped in
each domain, then you are group 1. The 'http' mechanism can do the job for
you.
If you do not have TXT record capability and have some domains that do not
have a webserver, then you are correct that you do not fit into either of the
two groups. Here's the situation you would be in:
In the recommended 'default SPF record' I gave, there was an mx mechanism
prior to the http one. This would mean that you could only send SPF-compliant
mail via one of the MX hosts for these domains. If there are no MX records,
you cannot send (or receive) mail at all.
Thinking about it further, the recommended default should be:
"v=spf1 http http:www.%{d} mx default=unknown"
With this default, a lot of small single-hosted sites will be SPF-compliant
without having to do anything at all.
I think it is fair to trust the MX for a domain since if the host is trusted
to receive mail it should be trusted to send too. Where this is not true (ie
you have untrusted users that can call out on port 25) the admin can specify
!mx in either an SPF text record or an smtp-spf.txt file.
This leaves a tiny group that may be 'falsely trusted' - domains with no txt
dns capability, no webserver and untrusted, unrestrained users running
rampant on an MX host. Even then they can only forge mail from other users in
the same domain, whilst logged in to the machine. If that's a problem, it
belongs in the 'blacklist' category, not sender authentication.
- Dan
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