2.4 另外記住 TXT 也是 DNS entries 的一部分，DNS 生效需要 24~48 小時。
2.5 舉例，成功的設定 SPF 會讓 Google Mail Gmail 更不會誤判垃圾信件
Example BEFORE-SET-SPF-TXT "NEUTRAL"
未設定之前，判定為「中立」
代碼:
Received-SPF: neutral (google.com: 74.125.82.52 is neither permitted nor denied by domain of XXXXXXXX) client-ip=74.125.82.52;
Authentication-Results: mx.google.com; spf=neutral (google.com: 74.125.82.52 is neither permitted nor denied by domain of XXXXXXXXX) smtp.mail=XXXXXXXXX
Example AFTER-SET-SPF-TXT "PASS"
設定之後，判定為「認證通過」
代碼:
Received-SPF: pass (google.com: domain of XXXXXXXXX designates 74.125.82.52 as permitted sender) client-ip=74.125.82.52;
Authentication-Results: mx.google.com; spf=pass (google.com: domain of XXXXXXXXX designates 74.125.82.52 as permitted sender) smtp.mail=XXXXXXXXXXX
3. 設定反查
相較於正查: Host Name / Domanin --> IP Address
所謂的反查就是 IP Address --> Host Name / Domain Name
有一些 Mail server 會透過檢查反查來判定 SPAM 的分數。
設定反查在某些狀況可以降低被誤判的機率。
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