如何从邮件头获取发件服务器IP以开展SPF验证？

我需要执行SPF授权验证，为此得获取发件邮件服务器的IP地址。虽然有“多条Received字段时查看最后一条”的规则，但测试部分在线工具后发现它们并非始终遵循此规则。之后看到一篇帖子提到：“要找到邮件的真实发件方，必须找到最早的可信网关——即从上到下读取邮件头时的最后一条Received记录”，于是我查询了MX记录，但在此处产生了困惑。

示例邮件头与查询结果 #

某邮件头包含3条Received记录：

Received: by 2002:a05:6358:5292:b0:b2:cdb1:e2f7 with SMTP id g18csp109750rwa;
        Wed, 7 Sep 2022 23:51:25 -0700 (PDT)
Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41])
        by mx.google.com with SMTPS id g29-20020a50d0dd000000b0044e7ab672f9sor5845875edf.52.2022.09.07.23.51.24
        for <pericapero1@gmail.com>
        (Google Transport Security);
        Wed, 07 Sep 2022 23:51:25 -0700 (PDT)
Received: from v6928srv01.domain ([213.208.147.53])
        by smtp.gmail.com with ESMTPSA id d3-20020a17090694c300b0073dc4385d3bsm825021ejy.105.2022.09.07.23.51.23
        for <pericapero1@gmail.com>
        (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128);
        Wed, 07 Sep 2022 23:51:23 -0700 (PDT)

其返回路径为：

Return-Path: <info@jadranmoon.com>

查询jadranmoon.com的MX记录，结果如下：

nslookup -type=MX jadranmoon.com
    Server:  UnKnown
    Address:  192.168.100.1
    
    Non-authoritative answer:
    jadranmoon.com  MX preference = 1, mail exchanger = aspmx.l.google.com
    jadranmoon.com  MX preference = 10, mail exchanger = alt4.aspmx.l.google.com
    jadranmoon.com  MX preference = 5, mail exchanger = alt2.aspmx.l.google.com
    jadranmoon.com  MX preference = 5, mail exchanger = alt1.aspmx.l.google.com
    jadranmoon.com  MX preference = 10, mail exchanger = alt3.aspmx.l.google.com
    
    jadranmoon.com  nameserver = ns4.domaintechnik.at
    jadranmoon.com  nameserver = ns1.domaintechnik.at
    jadranmoon.com  nameserver = ns2.domaintechnik.at
    jadranmoon.com  nameserver = ns3.domaintechnik.at

具体困惑 #

我无法理解这些MX记录的含义，原本预期会找到类似mx.google.com的结果，因此认为最后一个可信网关是倒数第二条Received记录（因包含“by mx.google.com”），并打算针对jadranmoon.com域名和209.85.220.41IP地址执行SPF检查，但遇到此类MX记录时我该如何操作？

内容的提问来源于stack exchange，提问作者lembnjetina