SpamAssassin, checks SPF records. You will find the default settings in the file 25_SPF.cf and the corresponding scores in the file 50_scores.cf. Both files can be found in the directory "C:\ProgramData\JAM Software\spamdService\sa-rules\updates_spamassassin_org".
If you are using the Exchange Server Toolbox or SmartPOP2Exchange, we recommend using the built-in editor to create customised SpamAssassin configuration files. You can find this under the Spam options. You can customise the scores of the SPF rules to your own requirements. To do this, add "score" followed by the name of the rule, followed by the new score in the configuration file: "score RULE_NAME 3.8".
Alternatively, you can also manually create your own .cf file in which you define your rules. Please note that this file should come last in alphabetical order, as SpamAssassin analyses the .cf files in numerical-alphabetical order. An example of the file name could be XMySettings.cf. For detailed information and instructions on writing rules in SpamAssassin, you can consult the official article in the SpamAssassin documentation. Here is the direct link to the article: Writing Rules in SpamAssassin
Don't forget to enter the SPF records in your MX record to ensure optimal functionality.
You can test spoofing using www.sendanonymousemail.net. This tool allows you to send anonymous emails, which can be useful for testing purposes.
Please note that this tool must not be misused for illegal activities or for sending spam. It is important to act responsibly and in accordance with applicable laws. Misuse can lead to serious legal consequences.
You can find more information about the possibilities with SpamAssassin on the official website: Apache SpamAssassin Wiki