1. IP addresses

DNS records

この部分は理解しがたい言葉を含んでいる。二月を待って、試す。

https://x.com/azumakuniyuki/status/1749348762907259320?s=20

正逆一致したアドレスから送ることとSPF条件を満たすこととは両立させづらい。DNS/運用/SPF

Requirements for all senders
  * Ensure that sending domains or IPs have valid forward and reverse DNS records, 
    also referred to as PTR records. Learn more

sending domains がなにを指すのか。(解説では sending hostname とある。)

Your sending IP address must have a PTR record. 
PTR records verify that the sending hostname is associated with the sending IP address. 

Every IP address must map to a hostname in the PTR record. 
The hostname specified in the PTR record must have a forward DNS that refers to the sending IP address.

Set up valid reverse DNS records of your sending server IP addresses that point to your domain. Check for a PTR record with the Google Admin Toolbox Dig tool.

Important: The sending IP address must match the IP address of the hostname specified in the Pointer (PTR) record.

SPFレコードのチェックに使用されるドメインはMAIL FROMコマンドで送られるドメイン (あるいは HELO host)

• エンベロープFromとReturn-Pathヘッダに現れる。

1.1. IP addresses

ここの要請なら、分からなくもない。

1. Your sending IP address must have a PTR record.
   • PTR records verify that the sending hostname is associated with the sending IP address. Every IP address must map to a hostname in the PTR record.
2. The hostname specified in the PTR record must have a forward DNS that refers to the sending IP address.

Set up valid reverse DNS records of your sending server IP addresses that point to your domain. Check for a PTR record with the Google Admin Toolbox Dig tool.

Important: The sending IP address must match the IP address of the hostname specified in the Pointer (PTR) record.

1.2. Shared IP addresses

A shared IP address (shared IP) is an IP address used by more than one email sender. The activity of any senders using a shared IP address affects the reputation of all senders for that shared IP.

A negative reputation can impact your delivery rate.

If you use a shared IP for sending email:

• Make sure the shared IP address isn’t on any internet blocklist. Messages sent from IP addresses on a blocklist are more likely to be marked as spam. If you use an email service provider for your shared IP, use Postmaster Tools to monitor the reputation of the shared IP address.

1.3. IP

https://support.google.com/mail/answer/10336 'The IP you're using to send email is not authorized...'

In order to prevent spam, Gmail refuses mail from IP addresses that are not authorized to send mail.

The determination of whether or not an IP address is authorized to send mail is made by the ISP that provides you with the IP address.

This list typically contains consumer IP ranges offered for dialup, DSL, or other broadband access.

SPF ?

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