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Question

All emails in 2026 show the same content (a scam email).

This happens on:

• Outlook Web
• Edge browser
• Outlook mobile app

When I open or reply to any email from 2026, the same scam email content appears.

Emails from 2025 and earlier display normally.

It looks like the mailbox index may be corrupted.

Answer 1

Microsoft Q&Aは、Microsoft製品についてユーザー同士などが課題解決に向けて情報の提供をしあうフォーラム(掲示版)です。
Outlook.comメールサービスの管理者はいませんし、管理者にエスカレーション出来る人もいません。

サーバー側での不具合を心配されているのであれば、下記を参照してチャットサポートなどを受けてみてください。
Outlook.comのサポートを受ける方法

二段階認証／Authenticatorの設定をしていなかったのでは？
そして、Microsoftアカウントに不審なサインイン履歴があるのでは？
申告されている事象については、ハッキングされた場合に発生しそうな事象だと思います。
（それ以外の要因の有無については分かりません。）

Answer 2

Disclaimer: I noticed that you posted your question in the (ja-jp) region in (English). For your convenience, my response will be in (English), but if you would prefer to use Japanese, please let me know. Thank you for your understanding.

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Hi 恵美子 坂本,

Welcome to Microsoft Q&A.

Based on the behavior you’re describing, scam or unexpected text appearing consistently across Outlook on the web, Edge, and the Outlook mobile app, this is much more likely related to account‑level settings rather than a local browser cache or device issue.

Here are the key things I’d recommend checking:

1. Review Outlook rules and forwarding (very important)

Attackers often create hidden or subtle rules after gaining access to an account.

In Outlook on the web:

• Go to Settings (⚙️) > Mail > Rules
• Carefully review all rules
• Delete anything you don’t recognize, especially rules that:
  • Move or delete messages
  • Redirect or forward mail
  • Apply broadly (for example, no specific sender conditions)

Also check Settings > Mail > Forwarding and make sure forwarding is disabled unless you explicitly set it up.

2. Check signatures and compose templates

Another common sign of compromise is unexpected content being injected into the signature or compose template.

In Outlook on the web:

• Go to Settings (⚙️) > Accounts > Signatures
• Remove any text, links, or formatting you didn’t add yourself
• Save the changes and test composing a new message

If the scam text appears automatically when composing, this strongly points to a signature or template configuration.

3. Review recent sign‑in activity and secure the account

I strongly recommend reviewing your Microsoft account sign‑in history:

• Visit the Recent activity page on your Microsoft account
• Look for unfamiliar locations, devices, or sign‑ins

If you see anything suspicious:

• Change your password immediately
• Re‑secure the account (update security info, enable or confirm MFA)

This aligns with known patterns where attackers add inbox rules or modify settings after unauthorized access.

4. Refresh Outlook on mobile

After cleaning up rules and signatures:

• In the Outlook mobile app, go to Settings
• Remove the affected account
• Add it back again to force a fresh sync of server‑side settings

If you notice rule names, conditions, or signature content you didn’t create, that’s a strong indicator the account was previously compromised, even if it now appears normal.

Feel free to share what you find after checking these areas, and we can take a closer look at next steps if needed.

Please let me know if this proves useful to you, or if you would like further assistance.

I'm looking forward to your reply.

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