Microsoft: Some Outlook.com users can't send emails with attachments

In a Monday advisory, Microsoft warned Outlook.com users about issues they might encounter when sending emails containing attachments.

Outlook.com users impacted by this known issue are seeing "Error code 550 5.7.520 Message blocked" errors when trying to send emails.

"Some users may not be able to send emails that contain attachments from their Outlook.com mailbox," the company said.

Redmond suggested an alternative method that enables affected users to share files: uploading them to OneDrive and sharing the link with the intended recipients.

To implement this workaround, users must click the attachment button while composing their message and click OneDrive to add previously uploaded files or the 'Upload and share' button to add the attachment to their online storage drive.

Alternatively, those affected by this issue could copy the link of an Office or OneDrive file and paste it directly into their email.

Microsoft also provides step-by-step instructions to guide users through this process:

Compose a new email message or calendar event. Select 'Attach': If the file is already in OneDrive, choose OneDrive. If the file is not in OneDrive, select Upload and share. Choose the item(s) to attach and click 'Share link.'

This temporary workaround will enable users to share files via email while Microsoft is working on addressing the underlying issue.

In July, Microsoft resolved another known issue triggering 401 exception errors and preventing Outlook.com users from searching their emails.

At the time, impacted users also reported having issues contacting Microsoft 365 support and being caught in a loop of sign-in and Office 365 service choice prompts.

One month earlier, Redmond fixed another issue blocking customers across the Americas from accessing their Exchange Online mailbox through Outlook on the web.

Last year, in October 2022, the company also addressed login issues affecting some Outlook for Microsoft 365 customers using their Outlook.com accounts.