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Gmail 將會提示沒有支援 STARTTLS 的信箱

Gmail 界面將會提示不支援 STARTTLS 的信箱:「Making email safer for you」。

先確認 msa.hinet.net 的 MX record:

;; ANSWER SECTION:
msa.hinet.net.          86174   IN      MX      0 msa-smtp-mx1.hinet.net.
msa.hinet.net.          86174   IN      MX      0 msa-smtp-mx2.hinet.net.

以及不支援 STARTTLS (在 EHLO 後不會出現 STARTTLS 選項):

$ t msa-smtp-mx1.hinet.net 25
Trying 168.95.6.53...
Connected to msa-smtp-mx1.hinet.net.
Escape character is '^]'.
220 msa.hinet.net ESMTP Sendmail 8.14.2/8.14.2; Thu, 11 Feb 2016 04:52:16 +0800 (CST)
EHLO localhost
250-msa.hinet.net Hello 114-32-152-63.HINET-IP.hinet.net [114.32.152.63], pleased to meet you
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-8BITMIME
250-SIZE
250-DSN
250-ETRN
250-DELIVERBY
250 HELP
QUIT
221 2.0.0 msa.hinet.net closing connection
Connection closed by foreign host.

打開 Gmail 在收件人的地方輸入 test@msa.hinet.net 後,就會跳出紅色鎖頭表示不支援 STARTTLS。

Gmail 將會針對沒有加密傳輸收到的信件標示警告

前陣子在「STARTTLS 的不完整性以及大規模監控電子郵件」提到現有的標準無法確保 ESMTP 一定會啟用 STARTTLS。所以 Google 正在跟 M3AAWG 研究標準來保護這類攻擊:

First, we found regions of the Internet actively preventing message encryption by tampering with requests to initiate SSL connections. To mitigate this attack, we are working closely with partners through the industry association M3AAWG to strengthen “opportunistic TLS” using technologies that we pioneered with Chrome to protect websites against interception.

另外一方面,Google 之後也會將未透過 STARTTLS 傳輸的信件標示出來:

To notify our users of potential dangers, we are developing in-product warnings for Gmail users that will display when they receive a message through a non-encrypted connection. These warnings will begin to roll-out in the coming months.

Google 的文章可以在「New Research: Encouraging trends and emerging threats in email security」這邊看到。

我的想像是 DNSSEC + TXT record 標示,不知道會不會走這條...

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