您好：　請問如下
是否　是5.7.26 DKIM 　問題
謝謝

主旨
Returned mail: see transcript for details

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The original message was received at Wed, 10 May 2023 11:03:57 +0800 from [192.168.100.15]

----- The following addresses had permanent fatal errors ----- XXXX8@gmail.com
(reason: 550-5.7.26 This mail is unauthenticated, which poses a security risk to the 5.7.26 sender and Gmail users,
and has been blocked.
The sender must 5.7.26 authenticate with at least one of SPF or DKIM.
For this message,5.7.26 DKIM checks did not pass and S...m.tw]
did 5.7.26 not pass with ip: [202.XXX.XXX.XXX].
The sender should visit 5.7.26 https://support.google.com/mail/answer/81126#authentication
for instructions on setting up authentication. X.......525 - gsmtp)

----- Transcript of session follows ----- ... while talking to gmail-smtp-in.l.google.com.:

DATA
<<< 550-5.7.26 This mail is unauthenticated,
which poses a security risk to the <<< 550-5.7.26 sender and Gmail users, and has been blocked.
The sender must <<< 550-5.7.26 authenticate with at least one of SPF or DKIM. For this message,
<<< 550-5.7.26 DKIM checks did not pass and SPF check for [fslivestock.com.tw] did
<<< 550-5.7.26 not pass with ip: [202.XXX.XXX.XXX].
The sender should visit <<< 550-5.7.26 https://support.google.com/mail/answer/81126#authentication for
<<< 550 5.7.26 instructions on setting up authentication. X.......525 - gsmtp
554 5.0.0 Service unavailable

看來，你並沒有完成 SPF/DMARC及DKIM ，貴司的信箱並未獲得認可，所以信件量一多，就擋！
另，郵件群發切勿使用同時並列收件人，這也是被擋的常見情況，我的習慣是，一封信一個使用者，或使用密件副本BCC取代收件人也可以達到同樣一信一人的效果

貴司的信箱主機並未被認可(所以我才叫你去做SPF/DMARC/DKIM)

怎麼做，長篇大論，問ChatGPT / Bing吧！

簡單的講，你必需要有DNS的控制設定權，如果沒有，沒輒！
而且，信箱絕不能使用浮動IP發信，如果會，一定要固定下來，否則必擋