查證過你的IP正反解已沒問題, 這部份也不影響IP評譽, SOA若能定義 SPF 會更好.

您的困擾, 我猜測問題應該在於, dell.com 使用的 Ironport (mail filter),
所參考的IP資料庫與官網的更新有落差造成的,
請您直接向 senderbase 反應:
說寄往 dell.com 的信會回應rejected due to low Senderbase reputation 被退,
但 senderbase.org 官方資料庫卻查得 Email Reputation 為 Neutral ,
請他們調查並進行處理.
http://www.senderbase.org/support/ 按 [ No, I need more ]

急於解決退信問題的話, 我贊同 u8526425 的補充,
把寄往 dell.com 及 3M.com 的信件,
轉由 hinet 提供的 smart-relay 代為轉信即可解.
( 是的, 3m.com 也用 senderbase mail filter )

順便發現HINET在IP的正反解處理上有嚴重暇疵(又是寇絲當造成嗎?),
以 210.242.25.110 為例,
它有 PTR record 為 210-242-25-110.HINET-IP.hinet.net ,
但 210-242-25-110.HINET-IP.hinet.net 卻查不出答案
Host 210-242-25-110.HINET-IP.hinet.net not found: 3(NXDOMAIN)
就是說, 如用戶沒有刻意指定反解, 那麼預設
210.242.25.xxx 會得到 210-242-25-xxx.HINET-IP.hinet.net
但負責 HINET-IP.hinet.net 這層的NS ,
卻完全回不出 210-242-25-xxx.HINET-IP.hinet.net 的 A Record .

https://www.senderbase.org/support/#problem=7
How long does it take for my IP to recover?
In general, once all issues have been addressed (fixed), reputation recovery can take anywhere from a few hours to just over one week, depending on the specifics of the situation and how much email volume the IP sends. Complaint ratios determine the amount of risk for receiving mail from an IP, so logically, reputation improves as the ratio of legitimate mails increases with respect to the number of complaints. Speeding up the process is not really possible. SenderBase Reputation is an automated system over which we have very little manual influence.

In the meantime, if there are recipients whom you cannot contact, we would recommend contacting the ISP involved to request temporary whitelisting or you can always arrange to contact the recipient via alternative means.

gary1198你好

想請問您的isp是哪一家的呢？
因為我們之前才有這部份問題，我們是根據使用的ISP去申請正反解，
申請完成一致了就不會寄不過去或寄不過來了！