February 2024
Beginner to intermediate
304 pages
9h 13m
Japanese
Content preview from 実務で使える メール技術の教科書 基本のしくみからプロトコル・サーバー構築・送信ドメイン認証・添付ファイル・暗号化・セキュリティ対策まで
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5
−
2
—
—
送信者の認証による対策
この本文中に書かれている「550-5.7.26」というエラーコードは、送信元
のメールサーバーが信頼できないことを意味しています。つまり、SPF の設
定と異なるサーバーから送信すると、受信者側で迷惑メールに振り分けられる
どころか、送信すらできない（宛先のメールサーバーが受け付けてくれない）
ようになりつつあります。
■ From を偽装し SPF を無効にする
SPF を指定すると、送信者が正規のメールサーバーを使用して送信してい
ることを受信側のメールサーバーで検証できます。しかし、SPF を使用して
いない偽のメールサーバーを使用して、エンベロープ From に適当なメール
アドレスを指定すると、SPF のチェックは行われません【図 5-8】。
たとえば、図 5-8 の上の例では、正規の利用者は DNS サーバーで SPF を
図 5-8
SPF のチェック
エンベロープFromとSPFが
一致しないためNG
？
【偽装した利用者】
エンベロープ
From:taro@example.com
ヘッダーの
From: taro@example.com
SPF
example.comのDNSサーバー
spf＝pass
spf＝fail
【正規の利用者】
エンベロープ
From:taro@example.com
ヘッダーの
From: taro@example.com
エンベロープFromに
対応するSPFがないため
チェックしない
【偽装した利用者】
エンベロープ
From:hacker@example.net ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.