Outlook blocked this attachment

“A coworker sent a .msg / zip and Outlook greyed it out as blocked.”

Outlook desktop with a blocked attachment banner and greyed file chip.

Likely cause

Classic Outlook blocks certain extensions (Level 1) or Microsoft 365 Safe Attachments is holding the file for scan. This is policy, not a corrupt mailbox — forcing “unblock all” via registry is the wrong first move on a work PC.

Confidence 80%Windows · Outlook desktop

1
Read which policy fired
Hover the greyed attachment. Note whether Outlook says it is a blocked file type or “Safe Attachments is scanning.” Those are different fixes.
2
Ask for a safer package
Have the sender re-send as a OneDrive / SharePoint link, or zip with a password shared out of band. Prefer cloud links over executable-looking extensions.
3
Use Outlook on the web if policy allows
Open outlook.office.com, find the same message, and try Download. Some tenants allow web download when desktop Level 1 blocks.
4
Escalate to IT — do not edit Level1Remove
If this is a legitimate business file type your team needs often, ask IT to adjust the attachment policy. Editing Outlook’s Level1Remove registry value on a managed PC usually violates policy.

Diagnose my screenshot

← All examples Next example: Excel says file is locked by another user →