Meng,
MWW> HELO domain.com
MWW> MAIL FROM:<user(_at_)domain(_dot_)com>
MWW> In this situation, an SPF record could easily become
MWW> unnecessarily complex for HELO purposes.
MWW> domain.com. TXT "v=spf1 include:this include:that a mx ?all"
MWW> If the domain admin changes the HELO string to be:
MWW> HELO mta1.domain.com
MWW> MAIL FROM:<user(_at_)domain(_dot_)com>
Actually, this is a remarkably concise demonstration of the problem
inherent with trying to multiplex two, entirely separate semantics into
the same record.
The way to solve it is not to dictate to users how they administer
their namespace, such as telling them what kinds of names to use in
HELO strings.
Rather, it is to separate the mechanisms that have different
semantics.
d/
--
Dave Crocker <mailto:dcrocker(_at_)brandenburg(_dot_)com>
Brandenburg InternetWorking <http://www.brandenburg.com>
Sunnyvale, CA USA <tel:+1.408.246.8253>, <fax:+1.866.358.5301>