https://www.cloudflare.com/ja-jp/learning/dns/dns-records/dns-dkim-record/

DNSのDKIMレコードとは？

DKIMレコードは、電子メールの真正性を確認するために使用される公開鍵を登録する、特殊なDNS TXTレコードです。

1. history

DKIMの仕組みにとは？

DKIMには主に2つの側面があります。
ドメインのDomain Name System（DNS） レコードに保存されるDKIMレコードと、
ドメインからのすべての電子メールに挿入されるDKIMヘッダーです。

2. record

k100430._domainkey.example.co.jp IN TXT "v=DKIM1; ...

3. Verifying DKIM and SPF records

Modified on: Sat, 6 Oct, 2018 at 8:38 PM https://support.duocircle.com/support/solutions/articles/5000792012-verifying-dkim-and-spf-records

Send an email to check-auth@verifier.port25.com

You will get an email back that looks like this:

Date: Sun, 4 Feb 2024 00:00:45 +0000
From: auth-results@verifier.port25.com
To: tmaeno@m.qmail.jp
Subject: Authentication Report
Return-Path: <auth-results@verifier.port25.com>
In-Reply-To: <20240204000152.GA17793@m.qmail.jp>

This message is an automatic response from Port25's authentication verifier
service at verifier.port25.com.  The service allows email senders to perform
a simple check of various sender authentication mechanisms.  It is provided
free of charge, in the hope that it is useful to the email community.  While
it is not officially supported, we welcome any feedback you may have at
<verifier-feedback@port25.com>.

Thank you for using the verifier,

The Port25 Solutions, Inc. team

==========================================================
Summary of Results
==========================================================
SPF check:          pass
"iprev" check:      pass
DKIM check:         none

==========================================================
Details:
==========================================================

HELO hostname:  mx.m.qmail.jp
Source IP:      14.192.44.5
mail-from:      tmaeno@m.qmail.jp

----------------------------------------------------------
SPF check details:
----------------------------------------------------------
Result:         pass
ID(s) verified: smtp.mailfrom=tmaeno@m.qmail.jp

DNS record(s):
    m.qmail.jp. 300 IN TXT "v=spf1 a:a.ns.qmail.jp mx ~all"
    a.ns.qmail.jp. 300 IN A 14.192.44.5

----------------------------------------------------------
"iprev" check details:
----------------------------------------------------------
Result:         pass (matches mx.m.qmail.jp)
ID(s) verified: policy.iprev=14.192.44.5

DNS record(s):
    5.44.192.14.in-addr.arpa. 300 IN CNAME 5.0/27.44.192.14.in-addr.arpa.
    5.0/27.44.192.14.in-addr.arpa. 300 IN PTR mx.m.qmail.jp.
    mx.m.qmail.jp. 300 IN A 14.192.44.5


----------------------------------------------------------
DKIM check details:
----------------------------------------------------------
Result:         none (message not signed)
ID(s) verified: 

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