"554 5.6.0 Invalid message content" when sending a message that contains an Excel or Word attachment

Original KB number: 2984127

Problem

A Microsoft 365 user creates an Excel spreadsheet (.xlsx file) or a Word document (.docx file), and then sends it as an attachment to an email message. However, the message and the attachment aren't delivered to the recipient, and the sender receives a nondelivery report (NDR) that contains the following error code:

554 5.6.0 Invalid message content

Cause

This issue may occur if the following conditions are true:

• A transport rule is set up that has the Defer the message if rule processing doesn't complete option enabled.
• During text extraction, the scanning process timed out when inspecting the attachment.

Workaround

To work around this issue, do one of the following:

• Password-protect the message before you send it.
• Disable the Defer the message if rule processing doesn't complete option in the transport rule. This option may be set on any rule in the rules list. For more info about how to modify transport rules in Exchange Online, see Manage transport rules.
• Review the message itself (obtain it if you are troubleshooting for someone else) and obtain a message trace to see if that provides additional insight.

More information

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