如果 'all' 不存在，SPF 记录的默认操作是什么？
What is the default action for an SPF record if 'all' is absent?
如果我有像这样的 SPF 记录：
v=spf1 +a a:spf2.example.com ip4:104.130.122.xxx/23
如果省略最后的 all 参数，记录中未提及的源的默认策略是什么？
RFC7208 section 4.7 定义默认机制：
If none of the mechanisms match and there is no "redirect" modifier,
then the check_host() returns a result of "neutral", just as if
"?all" were specified as the last directive.
如果我有像这样的 SPF 记录：
v=spf1 +a a:spf2.example.com ip4:104.130.122.xxx/23
如果省略最后的 all 参数，记录中未提及的源的默认策略是什么？
RFC7208 section 4.7 定义默认机制：
If none of the mechanisms match and there is no "redirect" modifier, then the check_host() returns a result of "neutral", just as if "?all" were specified as the last directive.