Spam and other bad types of email has grown by orders of magnitude over the recent years.  Even with filtering and spam folders many people have found the volume of spam unmanagable. There are a number of newer techniques that have been created in the past few years to fight these problems. "SPF" (Sender Policy Framework) is one of those. Not all email providers use it.  The Digital West mail servers are using SPF among other techniques to reduce spam and phishing emails.

SPF uses a record in the DNS for the sending domain to indicate what mail servers might be legitimate sources for email having that domain.  There are three basic variations. 

1. The strict " -all " syntax means that only the listed servers are allowed to send email as that domain.  Mail coming from other sources should be considered bogus.  The Digital West mail servers will reject messages which are not identified in the SPF record when -all is used.
2. The neutral "?all" version means that mail from the listed servers should be legitimate, but other sources may potentially be used to send emails on behalf of that domain.  This syntax helps deliverablity when the source matches one from the SPF record, but is not as effective as the strict version if used with large volume mailings.
3. There is also a transition syntax "~all"  which should cause a "Softfail" when the sending mail server is not in the SPF.  The Digital West mail servers will assign spam points for such messages delivered to the primary mail server, while the backup mail server will respond with a temporary deferal to these. See http://support.digitalwest.net/KB/a162/why-was-spf-with-all-rejected.aspx for a discussion.

You can visit the http://www.openspf.org/ to learn more about SPF.

See   http://www.kitterman.com/spf/validate.html for tools to validate and check SPF records.