Frank Ellermann wrote on Sunday, February 04, 2007 2:04 AM -0600:
In theory it's possible to check outbound mail against your own
sending IPs, Julian invented that. SPF checks work best "at"
the border, you can test it on the sending side. MSAs could
use this trick, if they wish to identify plausible (no FAIL)
envelope senders.
Sure, but the MSA needs to have a list of acceptable return-path
domains, and preferably a list of mailboxes with their required
authentication credentials, regardless of what external domain owners
publish. Since you need that list anyway to keep you from open
relaying, SPF checking is redundant for this purpose. It does identify
potential rejections at the recipient, which is a reasonable thing to
do.
--
Seth Goodman
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