Attachment Issues

How to Fix Outlook Attachment Error 550.5.0.350

Camila Milosovich Oct 9, 2026 869 views

Question details

The user needs to resolve an email delivery failure caused by attachment restrictions that result in an error code.

How to Fix Outlook Attachment Error 550.5.0.350

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Sending an email with one or more file attachments to internal or external recipients.
Observed behavior: The email fails to send and returns an error 550.5.0.350, indicating that the recipient organization (or the outbound server) does not allow the attached file type.

Before you start

Verify the file extension of your attachment to ensure it is not a commonly blocked executable file (like .exe or .bat) and check that the total size of your email is well under the standard 25 MB limit.

Solution 1Recommended

Compress the File or Use Cloud Sharing

Bypass direct file type restrictions and size limits by compressing your attachment into a ZIP archive or sharing a secure OneDrive link.

Many email servers automatically reject certain file formats for security reasons or block messages exceeding a specific size threshold. Wrapping the file in a compressed folder or hosting it on the cloud ensures smooth delivery.

Compress to a ZIP file

Locate the file on your computer, right-click it, select 'Send to', and choose 'Compressed (zipped) folder'. Attach this new ZIP file to your Outlook email instead.

Upload to OneDrive

If the file is too large, open your OneDrive folder or the OneDrive web interface, and upload the file there.

Share the link

Right-click the uploaded file in OneDrive, click 'Share', copy the sharing link, and paste this link into the body of your Outlook email.

Alternative Formats: If compressing the file doesn't work, consider converting your document to a universally accepted format like PDF before attaching it.

Solution 2

Test Using Outlook on the Web

Determine if the restriction is a localized issue with your desktop email client by sending the message through the web version of Outlook.

Solution 3

Contact Your Mail Administrator

If the error occurs for every single recipient you email, your own organization's outbound security policies might be blocking the file.

Free Microsoft Office alternative

Easily Create Safe Email Attachments with WPS Office

While WPS Office does not replace your email client, it provides a highly compatible and lightweight suite for handling documents securely. You can quickly save or convert your files into standard, safe formats like PDF, which rarely trigger email attachment filters like error 550.5.0.350.

1. Download the software: Visit the official WPS Office website to download the free suite for your operating system.
2. Open your document: Launch WPS Office and open the file you originally tried to attach in Outlook.
3. Export as PDF: Click on 'Menu', select 'Export to PDF', and save the new file to your computer. Attach this safe PDF to your email.

Completely free and lightweight Office suiteExcellent compatibility with Microsoft Word, Excel, and PowerPoint formatsBuilt-in PDF converter to create secure, universally accepted email attachmentsFamiliar user interface requiring no learning curve

microsoft office alternative - wps office

Frequently Asked Questions

What does error 550.5.0.350 mean in Outlook?

This specific error code means your email was rejected by a server because it contained an attachment type that is explicitly blocked by the recipient's organization or your own outbound security policies.

What file types are commonly blocked by email servers?

Servers frequently block executable files (.exe), batch scripts (.bat), visual basic scripts (.vbs), and sometimes macro-enabled documents (.docm) to protect networks from malware and viruses.

What is the maximum attachment size limit for Outlook?

Most standard Outlook.com and Exchange accounts have a strict overall message size limit of approximately 25 MB, which includes the email text and all attached files combined.

Why do I get this error when emailing anyone, not just one specific person?

If you receive error 550.5.0.350 for every recipient, the restriction is almost certainly being enforced by your own email provider or company's IT administrator before the email even leaves your outbox.

Outlook & Email Problems