To set up support for Sender Policy Framework on your server:

1 Click the Server shortcut in the navigation pane.

2 Click the Mail icon in the Services group. The server-wide mail preferences screen will open on the Preferences tab.

3 Select the Enable SPF spam protection checkbox and choose an option from the SPF checking mode drop-down to specify how to deal with email:

• To accept all incoming messages regardless of SPF check results, select Create only Received SPF-headers, never block. This option is recommended.
• To accept all incoming messages regardless of SPF check results, even if the SPF check failed due to DNS lookup problems, select In case of DNS lookup problems, generate temporary errors.
• To reject messages from senders who are not authorised to use the domain in question, select Reject mail if SPF resolves to fail.
• To reject the messages that are most likely from senders who are not authorized to use the domain in question, Reject mail if SPF resolves to softfail.
• To reject the messages from senders who cannot be identified by SPF system as authorised or not authorised because the domain has no SPF records published, select Reject mail if SPF resolves to neutral.
• To reject messages that do not pass SPF check for any reason (for example, when sender's domain does not implement SPF and SPF checking returns the "unknown" status), select Reject mail if SPF does not resolve to pass.

4 To specify additional rules that are applied by the spam filter before the SPF check is actually done by the mail server, type the rules you need in the SPF local rules box. We recommend that you add a rule for checking messages against the open database of trusted senders. For example, include:spf.trusted-forwarder.org. For more information on SPF rules, visit the SPF Policy website.

5 To specify the rules that are applied to domains that do not publish SPF records, type the rules into the SPF guess rules box. Entering a/24 mx/24 ptr gives good results for spam filters scoring Received-SPF lines.

6 To specify a notice that is returned to the email sender when a message is rejected, type it into the SPF explanation text box. If no value is specified, the standard text will be used as a notification.

7 To complete the setup, click OK.