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How to Customize Exchange Online Rejection Messages in Other Languages

Guest Writer Sep 28, 2026 871 views

Question details

Administrators need to customize standard Exchange Online rejection messages or non-delivery reports (NDRs) to display in multiple languages.

How to Customize Exchange Online Rejection Messages in Other Languages

Product: Exchange Online
Device & OS: not provided
Scenario: Configuring email mail flow rules to provide customized, multilingual explanations when an email is rejected or undelivered.
Observed behavior: The standard system-generated rejection or non-delivery message remains largely in English, even when a custom explanation is provided.

Before you start

Ensure you have the necessary Exchange administrator permissions to access the Exchange admin center (EAC) and modify organizational mail flow rules.

Solution 1Recommended

Customize Rejection Explanations via Mail Flow Rules

Use the Exchange admin center to append a customized explanation in your preferred language when a message is rejected.

While Exchange Online generates much of the standard NDR text in English, you can append a customized explanation in any language by configuring a specific mail flow rule. This ensures the sender receives context in their native language alongside the system text.

Access Exchange Admin Center

Navigate to Mail Flow Rules

In the left-hand navigation pane, go to 'Mail flow' and select 'Rules'.

Create or Edit a Rule

Click the '+' icon to create a new rule or select an existing rule to edit the conditions under which an email should be blocked.

Set the Rejection Action

Under the 'Do the following' dropdown, select 'Block the message' and then choose 'Reject the message and include an explanation'.

Enter Multilingual Text

Type your custom rejection explanation in the desired language(s) and save the rule.

Customize Rejection Explanations via Mail Flow Rules

Solution 2

Use the New-SystemMessage Cmdlet (Exchange Server)

For on-premises Exchange Server environments, use PowerShell cmdlets to fully customize system messages by language code.

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Frequently Asked Questions

Why is my Exchange Online non-delivery report (NDR) still partly in English?

Exchange Online automatically generates core system messages and diagnostic information in English. While you can add a custom explanation via mail flow rules, the service restricts modifying the underlying structural system text for consistency and diagnostic purposes.

Can I set up different rejection messages for different countries?

Yes, you can create multiple mail flow rules that trigger based on the sender's location, domain, or specific email attributes. This allows you to provide a localized explanation for senders in different regions.

Does the New-SystemMessage cmdlet work in Exchange Online?

Its functionality is heavily restricted in Exchange Online compared to an on-premises Exchange Server. Administrators managing Microsoft 365 tenants typically rely on mail flow rules to append custom text to standard NDRs.

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