Microsoft が提供する Microsoft 365 のサービス正常性（EX680695）にて、Exchange Online で外部からのメール メッセージの受信に遅延が発生する可能性のある SI（サービス インシデント）が発生していました。

“EX680695” のサマリー

目次

Users may be unable to access the Exchange Online service using Outlook on the web – EX502694

サービス：Exchange Online

状態：Service restored

ユーザーへの影響：Users may be unable to access the Exchange Online service using Outlook on the web.

Microsoft 365 のサービス正常性（EX680695）にて、Exchange Online で外部からのメール メッセージの受信に遅延が発生する可能性のある SI（サービス インシデント）が発生しています。

本事象の影響は、SMTP（Simple Mail Transfer Protocol）に特有のものになります。

ほとんどのユーザーでは、最大 1 時間の遅延の発生となっていましたが、場合によっては最大 24 時間程度の遅延が発生してい可能性があります。

さらに、メールの送信者には、”451 4.7.500 Server busy” というエラー メッセージを含む Non – Delivery Report（NDR）を受信した可能性があり、メールの再送信を行うとすると、最大 24 時間後に送信された可能性があります。

現在は、影響を引き起こすコードの問題を元に戻すことを目的とした修正プログラムの展開が完了しました。

なお、修正プログラムの展開が完了するまでの 1 時間程度の間に若干の遅延が発生していた可能性もありますが、現在はユーザーへの影響が緩和されていると思われます。

この問題は、IP アドレスのアンチ スパム ルールの適用を担うインフラストラクチャーの一部に適用された最近のアップデート内に問題のあるコードが含まれていたため、SMTP メール配信の遅延が発生していた問題になります。

今後は、このコードの問題がどのような経緯で含まれたについて分析し、アップデート時のテストおよび検証手順に確認できなかった要因も含めて調査しています。

なお、5 営業日以内に PIR（Post – Incident Report）が発行される予定です。

なお、この問題は影響を受けるインフラストラクチャーを経由してサービスの提供を受けている一部のユーザーに影響を与えていた可能性があります。

ただし、ワールドワイドのユーザーおよび一部の IP アドレスにのみ影響した問題のため、すべてのユーザーが影響を受けていた問題ではありません。

October 12, 2023 3:25 AM – Service restored

• ・Title : Some users may encounter delays sending and receiving external email messages in Exchange Online
• ・User impact : Users may have encountered delays sending and receiving external email messages in Exchange Online.
• ・More info : Impact was specific to Simple Mail Transfer Protocol (SMTP).
• Most users would have experienced up to a 1-hour delay; however, in some cases, users may have encountered delays of up to 24 hours.
• Additionally, the email sender may have received a Non-Delivery Report (NDR) with a “451 4.7.500 Server busy” error message, and their attempt to retry delivery of the email may have been delivered up to 24 hours later.
• ・Final status : We’ve completed our deployment of the change, which was a targeted reversion of the code issue causing impact.
• Users should now be experiencing mitigation, though some residual delays may still occur over the next hour as the change completes.
• ・Scope of impact : Impact was specific to some users who were served through the affected infrastructure.
• The issue affected users Worldwide and only for a portion of IP addresses, therefore not all users experienced impact.
• ・Start time : Tuesday, October 10, 2023 at 6:00 AM GMT+9
• ・End time : Thursday, October 12, 2023 at 2:00 AM GMT+9
• ・Preliminary root cause : A recent service update that was applied to a section of infrastructure responsible for enforcing IP address anti-spam rules contained a code issue, which was resulting in the delays with SMTP email delivery.
• ・Next Steps : – We’re further reviewing the recent update to understand how the code issue was introduced and to understand what prevented it from being detected in our update testing and validation procedures, which will allow us to prevent similar issues in future updates.
• We’ll publish a Post-Incident Report for this event within five business days.

October 12, 2023 2:47 AM・クイック更新 – Service restored

• We’ve completed our validation and have started to deploy the change to the affected environments.
• We anticipate users should start to experience relief within the next 30 minutes.
• This quick update is designed to give the latest information on this issue.

October 12, 2023 2:13 AM・クイック更新 – Service restored

• We’ve completed development of an additional fix which is undergoing validation prior to deployment.
• We expect to complete this process within the next 60 minutes.
• This quick update is designed to give the latest information on this issue.

October 12, 2023 1:27 PM – Service restored

• ・Title : Some users may encounter delays receiving external email messages in Exchange Online
• ・User impact : Users may encounter delays receiving external email messages in Exchange Online.
• ・More info : Impact is specific to Simple Mail Transfer Protocol (SMTP), and users may encounter delays of up to 24 hours.
• Additionally, the email sender may receive a Non-Delivery Report (NDR) with a “451 4.7.500 Server busy” error message, and their attempt to retry delivery of the email may be delivered up to 24 hours later.
• ・Current status : We’ve determined that our previous developed fix to resolve the throttling issue has proven to be unsuccessful.
• We’re developing a new fix that will undergo internal validation to ensure it resolves the underlying issue before deploying it to the impacted environments.
• ・Scope of impact : Impact is specific to some users who are served through the affected infrastructure.
• ・Start time : Tuesday, October 10, 2023 at 6:00 AM GMT+9
• ・Root cause : A recent service update, applied to a section of infrastructure responsible for enforcing IP address anti-spam rules, contains a change which is causing impact.
• ・Next update by : Thursday, October 12, 2023 at 3:30 AM GMT+9

October 11, 2023 11:22 PM – Service restored

• ・Title : Some users may encounter delays receiving external email messages in Exchange Online
• ・User impact : Users may encounter delays receiving external email messages in Exchange Online.
• ・More info : Affected users may see a “451 4.7.500 Server busy” error message.
• ・Current status : We’re progressing with the testing and development stage of our fix, to ensure its efficacy prior to deployment.
• We expect to be able to provide an estimate time of completion by the time of the next scheduled update.
• ・Scope of impact : Impact is specific to some users who are served through the affected infrastructure.
• ・Start time : Tuesday, October 10, 2023 at 6:00 AM GMT+9
• ・Root cause : A recent service update, applied to a section of infrastructure responsible for enforcing IP address anti-spam rules, contains a change which is inadvertently causing impact.
• ・Next update by : Thursday, October 12, 2023 at 1:30 AM GMT+9

October 11, 2023 9:22 PM – Service restored

• ・Title : Some users may encounter delays receiving external email messages in Exchange Online
• ・User impact : Users may encounter delays receiving external email messages in Exchange Online.
• ・More info : Affected users may see a “451 4.7.500 Server busy” error message.
• ・Current status : We’ve identified that a recent service update, applied to a section of infrastructure responsible for enforcing IP address anti-spam rules, contains a change which is inadvertently causing impact.
• We’re developing and validating a fix to revert to the most recent stable service version to remediate impact.
• In parallel, we’re continuing to manually add reported affected IP addresses to an allowed list to alleviate impact in the short term.
• ・Scope of impact : Impact is specific to some users who are served through the affected infrastructure.
• ・Start time : Tuesday, October 10, 2023 at 6:00 AM GMT+9
• ・Root cause : A recent service update, applied to a section of infrastructure responsible for enforcing IP address anti-spam rules, contains a change which is inadvertently causing impact.
• ・Next update by : Wednesday, October 11, 2023 at 11:30 PM GMT+9

October 11, 2023 7:26 PM – Service restored

• ・Title : Some users may encounter delays receiving external email messages in Exchange Online
• ・User impact : Users may encounter delays receiving external email messages in Exchange Online.
• ・More info : Affected users may see a “451 4.7.500 Server busy” error message.
• ・Current status : We’ve identified that specific IP addresses are being unexpectedly limited by our anti-spam procedures, causing inbound external email delivery to become throttled and delayed.
• We’re reviewing if there have been any recent changes to our anti-spam rules to understand why the IP addresses are being limited.
• In the meantime, we’re manually adding reported affected IP addresses to an allowed list to provide immediate relief.
• ・Scope of impact : Impact is specific to some users who are served through the affected infrastructure.
• ・Next update by : Wednesday, October 11, 2023 at 9:30 PM GMT+9

October 11, 2023 5:59 PM – Service restored

• ・Title : Some users may encounter delays receiving external email messages in Exchange Online
• ・User impact : Users may encounter delays receiving external email messages in Exchange Online.
• ・More info : Affected users may see a “451 4.7.500 Server busy” error message.
• ・Current status : We’re analyzing sample throttling IPs from simple messages to confirm whether the issue with the portion of SQL infrastructure is causing impact, before we begin formulating a remediation plan.
• ・Scope of impact : Impact is specific to some users who are served through the affected infrastructure.
• ・Next update by : Wednesday, October 11, 2023 at 8:00 PM GMT+9

October 11, 2023 1:52 PM – Service restored

• ・Title : Users are unable to receive external email messages within Exchange Online
• ・User impact : Users are unable to receive external email messages within Exchange Online.
• ・Current status : We’re currently reviewing simple messages to refine our understanding of this specific impact scenario and establish our troubleshooting steps.
• ・Scope of impact : Your organization is impacted by this event, as well as users who are attempting to receive external email messages within Exchange Online.
• ・Next update by : Wednesday, October 11, 2023 at 3:30 PM GMT+9

October 11, 2023 1:22 PM – Service restored

• ・Title : Users are unable to receive external email messages within Exchange Online
• ・User impact : Users are unable to receive external email messages within Exchange Online.
• ・Current status : We’re investigating a potential issue and checking for impact to your organization.
• We’ll provide an update within 30 minutes.

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