At 17:52 19/01/2009 Monday, you wrote:
Hi all,
I'd like to be comforted by usage statistics, but have no data. My
understanding of SPF checks by scope is as follows:
helo: could work always, however hostmasters don't usually add all
necessary DNS records; easily worked around using address literals.
not really as address literals may be RFC compliant, but no actual MTA would
really expect to survive using them,
thus most sites/servers doing spamfiltering of any sort only accept them from
internal-ranges
and smtp-submission-port clients
my own server responds with "your helo/ehlo was an address literal you can only
contact postmaster till your systems setup is complete"
on any of those {too few to mention {handfull a month} that arn't also on RBLS}
mfrom: provides some protection (proportional to adoption); requires
SRS or other machinery in case of forwarding; difficult to test and debug.
srs or per recipient {recipient-controlable} whitelists {which any decent MTA
in this day and age should do, many do even some of the big webmails}
not horribly difficult to test /debug many servers offer an echo@ address where
it will echo back a copy of the original with their spf headers added
pra: only works for bots, banks, or domains whose users never write to
a mailing list (unless the list adds resent-* headers; any?)
most mailinglists have worked with it {before pra even happened} for years {but
obviously the mailinglists it breaks are distribution lists such as
sales(_at_)company when its essentially a forward to many {thus no content
opened/modified on way through}
so easier to say pra broken by forwarding even if SRS is used
{requires newer SRS-+inject headers}
Visibility is easily worked around using resent-* headers.
if those headers present its the pra of the re-sender that is checked not the
original sender
so same requirement to list his/her mailhosts in the pra details for the resent
headers is still important
and adding arbitary resent-* headers won't work if the identities in them don't
have sender-id
Is that correct/agreed?
Article:
http://www.listbox.com/member/archive/735/2009/20090120053903:91507D60-E6DE-11DD-A795-A2E3A49B9427/
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