The only thing left to do is decide on the actual mechanisms and the format to use for the SPF text. The beginning will of course be "v=spf1 ", and it will end with "all" preceded by one of the following 3 characters which tell the mailserver how the domain holder wants SPF to be enforced.

- fail: this indicates that if none of the preceding mechanisms match, the email should be refused, as it comes from an invalid mailserver

~ softfail: this still indicates a fail, but that the email should not be refused on that basis but rather flagged as having failed the SPF check. This is useful for "rollout," the early stages of implementing SPF when the domain holder is not entirely sure how it is going to work, or for sorting failed email into a different folder.

? neutral: this indicates that SPF is being checked for reasons other than blocking email, and that nothing different should be done with the email on the basis of passing or failing the SPF check. It may be checked for statistics or other analysis, or it may be acted on by a subsequent process like the mail reader, but the mailserver itself does nothing differently based on the results of the SPF check.