Send & Receive Issues

How to Fix SMTP Error 550 5.7.520 in Hotmail (Message Blocked)

Partner Editor Oct 12, 2026 869 views

Question details

The user is unable to send emails, such as renewal notices, from a Hotmail account due to an SMTP 550 5.7.520 error indicating the message was flagged as spam.

How to Fix SMTP Error 550 5.7.520 When Sending Email from Hotmail

Product: Hotmail / Outlook.com
Device & OS: not provided
Scenario: Sending emails with attachments to multiple recipients simultaneously or repeatedly.
Observed behavior: Microsoft's spam filters block the outgoing message, return SMTP error 550 5.7.520, and prevent the email from being delivered.

Before you start

Ensure your internet connection is stable and verify that your Hotmail account has not been temporarily suspended for unusual sign-in activity before attempting these fixes.

Solution 1Recommended

Modify Message Content and Sending Behavior

Since Microsoft’s spam filter triggered the 550 5.7.520 error, adjusting your email content, attachments, and sending frequency is the most effective way to resolve the block.

Free Hotmail accounts are designed for personal use and have strict daily limits to prevent spam. Sending identical messages to multiple recipients, especially with attachments, often triggers these automated filters.

Simplify the Message Content

Review the email body and remove any suspicious links, excessive promotional language, or unusual formatting that might trigger automated spam filters.

Test Without Attachments

Remove the attached file and send a test email. If the email is delivered successfully, ensure your original attachment is scanned for malware, is a safe file type (like standard PDF), and does not exceed size limits.

Reduce Sending Frequency

Avoid sending identical messages to large groups of recipients at the same time. Send your emails in smaller, spaced-out batches to prevent your account from being flagged.

Wait Before Retrying

If your account has been temporarily blocked from sending, wait at least 24 hours before attempting to send new messages.

Spam Filter Limits: Hotmail enforces strict daily sending limits. Exceeding these limits or repeatedly trying to bypass a spam block can result in your account being permanently restricted.

Solution 2

Request Microsoft Support to Unblock the Account

If legitimate emails continue to be blocked after you have adjusted your content and sending habits, you must contact Microsoft to review and unblock your account.

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Create and Manage Your Renewal Documents Seamlessly with WPS Office

While resolving Hotmail SMTP limits, you might need a reliable tool to draft renewal notices, manage recipient lists, or export safe PDF attachments. WPS Office is a lightweight, free alternative to Microsoft Office that helps you create professional, spam-filter-friendly documents.

1. Download and Install: Get WPS Office from the official website and install it on your computer or mobile device.
2. Draft Renewal Notices: Use WPS Writer to draft your notices, utilizing free templates and saving them in highly compatible .docx formats.
3. Export to PDF: Click 'Export to PDF' to create safe, lightweight attachments that are less likely to trigger email spam filters.

Fully compatible with Microsoft Word, Excel, and PowerPoint formats.Easily export documents to lightweight, clean PDF attachments to avoid spam filters.Free, lightweight, and features a highly familiar user interface for quick adoption.Includes a powerful spreadsheet tool for securely managing your email recipient lists.

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Frequently Asked Questions

What does SMTP Error 550 5.7.520 mean in Hotmail?

This error indicates that Microsoft's automated spam filters have blocked your outgoing email. It usually happens when a message contains suspicious attachments, flagged links, or is sent to too many recipients at once.

Can I send bulk emails using a free Hotmail account?

Free Hotmail (Outlook.com) accounts are designed for personal use and have strict daily sending limits. If you need to send bulk emails, newsletters, or automated renewal notices, it is highly recommended to use a dedicated business email service or an email marketing platform.

How long does a Hotmail spam block last?

Temporary sending blocks typically last for 24 hours. If you continue to attempt sending the same flagged messages during this period, the automated system may extend the duration of the block.

Why is my PDF attachment triggering the spam filter?

Spam filters may flag attachments if they are exceptionally large, contain unusual metadata, or if the email body lacks sufficient text to provide context. Try compressing the PDF and adding a clear, personalized message to the email body.

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