How can I prevent, detect and block spoofing?
The SpamAssassin used checks SPF records. The default settings for SPF can be found in 25_SPF.cf or the corresponding scores in 50_scores.cf under "C:\ProgramData\JAM Software\spamdService\sa-rules\updates_spamassassin_org".
If you are using the Exchange Server Toolbox or SmartPOP2Exchange the best way to set your own scores is to use the built-in editor for creating custom SpamAssassin config files which you can find under Spam Options.
For more information about the options, see:
Alternatively, you can manually create your own .cf file in which you define your "rules", this should only come last alphabetically, since SpamAssassin will evaluate the cf files in numerical-alphabetical order. (For example XMySettings.cf).
Please note that you should add the SPF records to your MX record.