Outlook blocking emails

Question

Why is outlook blocking emails being sent by various third parties? I have verified the third party has the correct email address.

Answer 1

Outlook may block emails from third parties for several reasons, primarily related to security measures designed to protect users from spam, phishing, and other malicious activities. Here are some common reasons why emails might be blocked:

1. Blocked Senders List: If the third party's sending IP address has been identified as a potential threat, it may be added to a blocked senders list, preventing their emails from being delivered to Outlook users.
2. Spam Detection: Microsoft employs various anti-spam tools that can detect outbound spam from organizations. If the third party's IP address is flagged for sending spam, it can lead to blocking.
3. Email Authentication Failures: If the third party's email fails authentication checks (like SPF, DKIM, or DMARC), Outlook may block the email as a precaution.
4. Non-Delivery Reports (NDRs): If emails sent to Microsoft 365 recipients generate NDRs indicating access denied or blocked sender messages, this can be a sign that the sender is on a blocked list.

To resolve this issue, the third party can use the Office 365 Anti-Spam IP Delist Portal to request removal from the blocked senders list if they believe their emails are being incorrectly blocked. Additionally, they should ensure compliance with best practices for sending emails to avoid being flagged as spam.

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References:

• External senders - Use the delist portal to remove yourself from the blocked senders list and address 5.7.511 Access denied errors
• Microsoft 365 services for external email senders

Answer 2

Hi, I'm John! I will help you with this.

Outlook usually blocks emails for security reasons. It can be spam filtering, sender reputation, or account settings.

To help narrow down the issue:

1. Are the missing emails in Spam/Junk or Other folder?
2. Are they getting any bounce-back or error message?
3. Is this a personal Outlook.com account or a work/school account?

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In the meantime, I recommend checking out this Microsoft support article:

• "Can't send or receive email in Outlook.com" https://support.microsoft.com/office/can-t-send-or-receive-email-in-outlook-com-d39e3341-8d79-4bf1-b3c7-ded602233642 Please scroll down and take a look at the sections titled "Can’t receive mail in Outlook.com". It walks you through some helpful steps that usually resolve this kind of issue.
• Check your mailbox settings to confirm nothing is filtering or blocking those emails.
• Make sure your Focused Inbox is turned off, so all messages show in one place. https://support.microsoft.com/office/focused-inbox-for-outlook-f445ad7f-02f4-4294-a82e-71d8964e3978
• Try adding their email addresses to your Safe Senders list to make sure Outlook doesn’t block or redirect them. https://support.microsoft.com/office/add-recipients-to-the-safe-senders-list-in-outlook-be1baea0-beab-4a30-b968-9004332336ce

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Check any Outlook rules:

• In https://outlook.live.com/mail go to Settings > View all Outlook settings > Mail > Rules and Mail > Forwarding to make sure no one has set up rules to forward or delete your messages.

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If the issue persists, please provide more details by answering my questions.

Click "Add comment" below to let me know.

Regards,

John J.D.