Undelivered Mail Returned to Senderで550-5.7.26 This message does not pass authentication checks になる件


少し前からお客様がメール送信後「Undelivered Mail Returned to Sender」という見出しのエラーメールが私へ来るようになりました。


This is the mail system at host メールサーバURL.

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<Gメールのアドレス>: host gmail-smtp-in.l.google.com[IPアドレス] said:
550-5.7.26 This message does not pass authentication checks (SPF and DKIM both 550-5.7.26 do not pass). SPF check for [当社のドメイン] does not pass with ip: 550-5.7.26 [IPアドレス].To best protect our users from spam,
the message has 550-5.7.26 been blocked. Please visit 550-5.7.26
https://support.google.com/mail/answer/81126#authentication for more 550 5.7.26 information. x5-20020a656aa5000000b004ded554485bsi16091992pgu.663 -gsmtp (in reply to end of DATA command)


SPFレコードの設定方法 – お名前.comの場合