Send & Receive Issues

How to Fix Outlook Emails Rejected by Recipient Email Providers

Steven Parker Oct 14, 2026 869 views

Question details

The user needs to resolve an issue where outgoing Outlook emails are bouncing back and being rejected by the recipient's email provider.

How to Fix Outlook Emails Rejected by Recipient Email Providers

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Replying to existing email threads with known contacts, banks, and prospective employers.
Observed behavior: Microsoft generates a nondelivery report stating that the recipient's email provider rejected the message, causing the user to suspect their account has been blocked.

Before you start

Before proceeding, check your Inbox or Junk Email folder for a Non-Delivery Report (NDR) email from the Microsoft System Administrator, as this contains the specific diagnostic error code needed for troubleshooting.

Solution 1Recommended

Check the Non-Delivery Report (NDR) for Error Codes

The NDR provides the exact reason why the email was rejected, which is crucial for determining if your account is blocked or if there is a server issue.

When an email fails to deliver, Microsoft sends an automated bounce-back message. Analyzing this message helps identify if the block is due to suspicious activity, bulk-mail filters, or invalid recipient addresses.

Open the NDR message

Locate and open the bounce-back email message in your Outlook Inbox.

Locate the error code

Scroll through the automated message body to find the specific diagnostic error code (e.g., 5.1.10, 5.7.1, or 550).

Identify the block reason

Read the administrator notes in the email to see if it explicitly mentions your account being restricted for sending suspicious bulk emails or exceeding sending limits.

Check the Non-Delivery Report (NDR) for Error Codes

Common Error Codes: An error code like 5.7.1 often indicates a security block or unauthorized sender issue, while a 5.1.1 code typically means the recipient's email address is invalid.

Solution 2

Review Microsoft 365 Sending Limits

Outlook restricts the volume and frequency of outgoing messages to prevent spam, which can cause messages to be rejected if exceeded.

Solution 3

Contact Your IT Administrator or Microsoft Support

If replies to existing trusted threads are still blocked, your account may be restricted at the server level requiring administrator intervention.

Free Microsoft Office alternative

Try WPS Office for Seamless Document Management

While troubleshooting your Outlook email server issues, you can manage all your essential documents without interruption using WPS Office. It provides a lightweight, highly compatible alternative to Microsoft Office.

1. Download WPS Office: Visit the official WPS Office website and click the free download button.
2. Install the application: Run the downloaded installer file and follow the on-screen instructions to complete the setup.
3. Manage your files: Launch WPS Office to easily create, open, and edit documents, spreadsheets, and presentations.

Fully compatible with Microsoft Office formats, including DOCX, XLSX, and PPTX.Free and lightweight, consuming minimal system resources on your device.Familiar and intuitive user interface allowing for a seamless transition from Microsoft Office.Built-in robust PDF reader and editor for easily managing your email attachments.

microsoft office alternative - wps office

Frequently Asked Questions

Why are my Outlook replies to known contacts bouncing back?

If your account is flagged for suspicious activity or if you have exceeded Microsoft's daily sending limits, the server will temporarily block all outgoing messages. This block applies universally, meaning even emails sent as direct replies to trusted contacts or organizations will be rejected.

How do I read an Outlook Non-Delivery Report (NDR)?

Open the bounce-back email in your inbox and look for a specific diagnostic error code, typically starting with the number 5 (e.g., 5.1.10 or 5.7.1). This specific code explains whether the delivery failure was due to an invalid email address, a server rejection, or spam filtering restrictions.

Can my email account be blocked by Microsoft by mistake?

Yes. Microsoft's automated security algorithms can sometimes erroneously flag accounts if you travel to a new location, log in from a new unrecognized device, or send an unusually large email attachment. Contacting Microsoft Support or your IT administrator can help verify your identity and lift the restriction.

Outlook & Email Problems