已完成合规认证但注册验证邮件仍被Gmail标记为垃圾邮件的求助

我最近碰到一个棘手的问题：用SendGrid作为邮件中继配合Drupal发送邮件，已经配置了DKIM、DMARC、SPF、反向DNS所有能想到的合规认证项，还专门用了2个SendGrid专属IP，但Gmail偏偏把注册验证邮件频繁标记为垃圾邮件——其他同系统发送的事务邮件就没这么多用户反馈被标垃圾的情况。

我怀疑会不会是邮件内容的锅？比如主题里用了“email”和“password”这类敏感关键词？

下面是我用邮件测试工具拿到的完整邮件原始信息：

Received: by mail-tester.com (Postfix, from userid 500)
id 22962A0BA9; Thu, 7 Sep 2023 11:36:50 +0200 (CEST)
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on mail-tester.com
X-Spam-Level:
X-Spam-Status: No/0.5/5.0
X-Spam-Test-Scores: DKIM_SIGNED=0.1,DKIM_VALID=-0.1,DKIM_VALID_AU=-0.1,
DKIM_VALID_EF=-0.1,HTML_IMAGE_ONLY_20=0.7,HTML_MESSAGE=0.001,
SPF_HELO_NONE=0.001,SPF_PASS=-0.001,UNPARSEABLE_RELAY=0.001,
URIBL_BLOCKED=0.001
X-Spam-Last-External-IP: 149.72.70.96
X-Spam-Last-External-HELO: o2.ptr5494.generation.global
X-Spam-Last-External-rDNS: o2.ptr5494.generation.global
X-Spam-Date-of-Scan: Thu, 07 Sep 2023 11:36:50 +0200
X-Spam-Report:

• 0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was

• blocked.  See
  

• http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block
  

• for more information.
  

• [URIs: generation.global]
  

• -0.0 SPF_PASS SPF: sender matches SPF record
• 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record
• 0.7 HTML_IMAGE_ONLY_20 BODY: HTML: images with 1600-2000 bytes of

• words
  

• 0.0 HTML_MESSAGE BODY: HTML included in message
• 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily

• valid
  

• -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature
• -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from

• author's domain
  

• -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from

• envelope-from domain
  

• 0.0 UNPARSEABLE_RELAY Informational: message has unparseable relay

• lines
  

Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=149.72.70.96; helo=o2.ptr5494.generation.global; envelope-from=bounces+1455748-9606-test-noj289t8t=srv1.mail-tester.com@email.generation.global; receiver=test-noj289t8t@srv1.mail-tester.com
DMARC-Filter: OpenDMARC Filter v1.3.1 mail-tester.com 818F8A0BAE
Authentication-Results: mail-tester.com; dmarc=pass header.from=generation.global
Authentication-Results: mail-tester.com;
dkim=pass (2048-bit key; unprotected) header.d=generation.global header.i=@generation.global header.b=2xi/S5B1;
dkim-atps=neutral
Received: from o2.ptr5494.generation.global (o2.ptr5494.generation.global [149.72.70.96])
(using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
(No client certificate requested)
by mail-tester.com (Postfix) with ESMTPS id 818F8A0BAE
for test-noj289t8t@srv1.mail-tester.com; Thu, 7 Sep 2023 11:36:45 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=generation.global;
h=content-type:from:mime-version:subject:to:cc:content-type:from:
subject:to;
s=s1; bh=VNik7W3spVoPXOL9Pe/iAk8NWnAsTueGVG0bE354jWE=;
b=2xi/S5B1SjFcxSbsyqf4yBw1DyCg1kdglqBy2llbGUkuxlFMXeTJzCPKUh/7AuregHvS
PlgUrFWVtst2F5BjSlyb+7IiM6EY0thV8EQlhECkdWXZ/xX6+udHHbQ8uXcsTfB6w4ufvT
UXnTGrEMUgPlXF/Zi7dq1/bfUCwMg9jW85SMnuyKNJcSW26+h4euaQTCmIKXVdMQax8LMs
qhMpQ5DJHGaQIE/QBqs/qrJT8ZXf2/CpKRup0+iCBcV/PLHV3TqK7iHBxOHfsRO0C+aZW8
AIXKVfVfBamTznoqK8pIaP3Pa0nY8OjWtyVdOM1QKDNeyC4f/YCghGagnZhtyyYg==
Received: by filterdrecv-d7bbbc8bf-r6vsn with SMTP id filterdrecv-d7bbbc8bf-r6vsn-1-64F999AB-1
2023-09-07 09:36:43.122578653 +0000 UTC m=+6193231.319333022
Received: from MTQ1NTc0OA (unknown)
by geopod-ismtpd-5 (SG) with HTTP
id s09u95VoQgCqnWJ62_6_Jw
for test-noj289t8t@srv1.mail-tester.com;
Thu, 07 Sep 2023 09:36:42.966 +0000 (UTC)
Content-Type: multipart/alternative; boundary=953f2f71d3cc057b35d2548e10420b0c12b9e8296557c5bdcb71f06a9ab3
Date: Thu, 07 Sep 2023 09:36:43 +0000 (UTC)
From: Generation Global helpdesk@generation.global
Mime-Version: 1.0
Subject: Confirm your email address and set your password
Message-ID: s09u95VoQgCqnWJ62_6_Jw@geopod-ismtpd-5
X-SG-EID:
=?us-ascii?Q?Xt7jwbpeS7ePvcb7wfzapY18feVwdv8y=2FNk3PHticMZ+mcfHuT+e1pqmHtpBqY?=
=?us-ascii?Q?qPxn5Sxq7E=2F=2FKSRpy9073cWUxl+s9D4ldWzZtxi?=
=?us-ascii?Q?BjIYIDiOEaSCFtP6GZmzY2G02sueFGVZCOX3huP?=
=?us-ascii?Q?38lIdgS3cqafS6cPSP0dAfb+GPmoUtHmrx+oCkE?=
=?us-ascii?Q?y7kHOCORoLpaYDeRHSxPjobmOiLM2YH7DGpteu=2F?=
=?us-ascii?Q?rVMnDT2ycQs5AhdPeH=2FVVPcpVL=2FKoam6mm5rXE3?=
=?us-ascii?Q?tl1pEsKdhSoiDdwhxuantJdXyQPpBmBxWSxd1Qg?= =?us-ascii?Q?nM4=3D?=
X-SG-ID:
=?us-ascii?Q?N2C25iY2uzGMFz6rgvQsb8fga5n54QRd+qJeKTHTMRl8SOyCCBCf3p5maOTknh?=
=?us-ascii?Q?gtwazv1EA7ampdFt8T+QCumT2O+RNz7DUll=2FRZt?=
=?us-ascii?Q?LIRdb9BI5nPn+Sv6n0WjfBvJc4yEbFDtfbPKLbB?=
=?us-ascii?Q?3QsIUQOFB1ZIjZuCnD8yn3YULXOIhEzhE7lRGtK?=
=?us-ascii?Q?aSOnEhCBgfv4XCMyoP2M4qmCDa70CPJ034eqczg?=
=?us-ascii?Q?3bGcY7d4D6yI55Pr0=3D?=
To: test-noj289t8t@srv1.mail-tester.com
X-Entity-ID: T2i3yDP3SaZzBBKZ1DMPgA==
--953f2f71d3cc057b35d2548e10420b0c12b9e8296557c5bdcb71f06a9ab3
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0

Dear Student,

Thank you for registering your account on Generation Global. Now we
just need you to confirm your email address so you can get started on
our site. Please click on the link below to confirm your email address
and set your password:

Confirm email and set password

[https://adventure.generation.global/student/reset/56170/1694079401/kwUczgz=
A5WnAsFB66rNpo-MzNYEzZ7QBT5uqsUW5QE0]

If you have any questions please contact our support at
generation.global/support [https://generation.global/support].

The Generation Global Team
--953f2f71d3cc057b35d2548e10420b0c12b9e8296557c5bdcb71f06a9ab3
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html; charset=us-ascii
Mime-Version: 1.0

Dear Student,

Thank you for registering your account on Generation Global. Now we just need you to confirm your email address so you can get started= on our site. Please click on the link below to confirm your email address and set your= password:

Confirm email and set pa= ssword

If you have any questions please contact our support at generation.global/support.

The Generation Global Team

<img src=3D"http://mail.generation.global/wf/open?upn=3DCGUeh9-2FN5rG1LZ-2B=
9pan7arSj-2Bi-2B25ICZny4hSCkMZ4rbSqMLteZiRPKm4CNWI44zwXM-2Ff2AmZJR4MvCiYPTn=
Go7LXnaq1lh0e9KJzkIYC-2B3RK5nlWSPSswcZdPr4m6Lhbhvsuq8sLsiLwbzfy0WGFpq3yp-2F=
pyCmCW8vvjP80Cp90SmhMoAfXn318qXjpv5gci6abl0VDtuzCB7xGU9CSvg1WCaXOENw124PU2b=
zghoPG5taQpR6Tl-2FRnGSbnYCJjy3AoANdwLKA-2FOvnVEZG5AcxYqVrTc9uvrWBRsdZoxvCjn=
GTZPQetMSfJiQMjDzgsGxqcwQMqLpHNk5ubYvXQDoCjk4OZxrJYRDzjsxSNCh90sfs56sFQgUre=
UC0T5d6OwpGDYF2J3KzgJxk2wzEPoWk-2B-2Bd75LrTx5lFim7B-2FLNePLLy1G9agM2QxA6WCg=
u7a8MD9HxNZ-2FLo5TDw23EvWsA-3D-3D" alt=3D"" width=3D"1" height=3D"1" border=
=3D"0" style=3D"height:1px !important;width:1px !important;border-width:0 !=
important;margin-top:0 !important;margin-bottom:0 !important;margin-right:0=
!important;margin-left:0 !important;padding-top:0 !important;padding-botto=
m:0 !important;padding-right:0 !important;padding-left:0 !important;"/>
--953f2f71d3cc057b35d2548e10420b0c12b9e8296557c5bdcb71f06a9ab3--

另外补充个奇怪的情况：第二次测试时，发现有一次DMARC居然失败了——但发送IP和之前通过DMARC验证的邮件完全一致，我实在搞不懂为什么会出现这种随机失败的情况。

有没有大佬能帮我分析下，为什么这些注册验证邮件会被Gmail标成垃圾邮件？

备注：内容来源于stack exchange，提问作者MultiformeIngegno