Monday, December 11, 2023

It’s not just you: a bug could prevent you from sending emails from Outlook

If you are not able to send emails from, calm down. It doesn’t just happen to you. Microsoft explained that some users might encounter an error when trying send messages that contain attachments.

Users affected by the Outlook failure see errors such as «Error code 550 5.7.520 Message blocked». The company has registered this problem since at least Monday, November 6. While they resolve the problem, he proposed as an alternative to send the files as a OneDrive link, instead of attaching them.

Last July, Microsoft faced another issue that caused 401 exception errors. This prevented users from searching for messages in their emails. In accordance with Bleeping Computeraffected people also had trouble contacting Microsoft 365 support. So they were stuck in a loop of Office 365 sign-in messages and service options.

In June, at least two other failures affected the Outlook service. One of them limited customers in the Americas from accessing their Exchange Online mailbox through the Outlook web. And the second, reached, Azure Portal and OneDrive. Microsoft then explained that the suspension was caused by DDoS attacks claimed by a threat actor known as Anonymous Sudan.

How to send files from Outlook while the failure lasts?

The bug that prevents sending emails from Outlook would only affect messages with attachments, according to Microsoft’s explanation. If you don’t know how to send a file as a link, follow these instructions:

  1. If the file is already on your OneDrive, choose OneDrive.
  2. If the file is not on OneDrive, select Upload and share.
  3. Choose the elements you want to attach and select Share link.
  4. You can also use Copy link from an Office or OneDrive file or paste it into your email.

Other users also reported another problem sending, specifically, PDF files from any Microsoft domain:,, or In these cases, apparently, the email was detected as spam and blocked from being sent. But the problem was already resolved this Tuesday morning.

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