-all means hard reject, ~all - soft reject, here's a quote :
Quote:
~all : SPF queries that do not match any other mechanism will return "softfail". Messages that are not sent from an approved server should still be accepted but may be subjected to greater scrutiny. If you need tight control replace ~all with -all (hard fail).
For example, following recored the "a" and "mx" specify the systems permitted to send messages for the given domain. The "-all" at the end specifies that, if the previous mechanisms did not match, the message should be rejected.
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Check the following :
host -t txt microsoft.com
Quote:
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microsoft.com descriptive text "v=spf1 mx include:_spf-a.microsoft.com include:_spf-b.microsoft.com include:_spf-c.microsoft.com include:_spf-ssg-a.microsoft.com ~all"
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Here's some general information.
