hcm-nc.jp 40%

https://transparencyreport.google.com/safer-email/overview?encrypt_region_table=&encrypt_region=region:142&lu=encrypt_region

0%

$ telnet anymx02.itmedia.co.jp 25
Trying 13.112.77.12...
Connected to anymx02.itmedia.co.jp.
Escape character is '^]'.
220 ESMTP Postfix
ehlo wk.qmail.jp
250-anymx02.itmedia.co.jp
250-PIPELINING
250-SIZE 15744000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 SMTPUTF8

1. TLS

/MTA-STS

メール通信経路の暗号化 https://logmi.jp/tech/articles/324439

https://sendgrid.kke.co.jp/blog/?p=12945

TLS(暗黙的TLS)は、初期接続でSecure Socket Layer（SSL）またはTransport Layer Security（TLS）証明書を使って開始されます。

StartTLSは、プレーンテキストでやり取りを開始し、可能であればTLSにアップグレードするプロトコルコマンドです。

配信中のメールの暗号化 https://transparencyreport.google.com/safer-email/overview?hl=ja

/587

/smtp.gmail.com example 主に Gmail から送信する場合のことが書かれている。

Require a secure connection for email

Set up TLS for specific email addresses and domains

Transport Layer Security (TLS) is a security protocol that encrypts email for privacy. TLS prevents unauthorized access of your email when it's in transit over internet connections.

1.1. whois

For inbound messages, the From: sender must exactly match an address or domain in the setting. 

Understand what happens to messages sent to or from servers that don't use TLS

Your Secure transports (TLS) compliance setting affects messages sent over non-TLS connections, 
for addresses and domains that you specify in the setting.

Outgoing messages       Messages aren't delivered, and will bounce. You'll get a non-delivery report. 
Gmail makes only one attempt to send messages over a non-TLS connection.

Incoming messages       Incoming messages from non-TLS connections are rejected without any notification to you. 
The sender gets a non-delivery report.

1.2. history

https://support.google.com/a/answer/7381367?sjid=15954232527167999829-AP

Use address lists to apply settings to specific people or domains

Use address lists in spam, content, and routing settings

As an administrator, you can create groups of email addresses and domains called address lists.
Address lists let you apply Gmail settings to specific email addresses or domains. 
Use an address list when you want to exclude select addresses or domains from settings, 
or apply settings to messages from or to select addresses or domains

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