How to receive ZIP files in Outlook 365

Question

I've been trying to resolve how to enable receiving of ZIP files. Been browsing around Exchange Admin without luck.

Blocking of ZIP files has been set on by Microsoft because this has been working earlier.

Anybody...?

Answer 1

Understanding the Problem

If you're unable to receive ZIP files in Outlook 365 (part of Exchange Online), it's usually because a security feature or policy is blocking them. Microsoft can block ZIP files by default due to the potential risk of malware being embedded inside them. Even if it worked before, recent security updates or policy changes might have activated restrictions.

Check Mail Flow Rules in Exchange Admin Center

Start by reviewing your mail flow rules in the Exchange Admin Center. Go to the Microsoft 365 Admin Center, access the Exchange Admin Center (EAC), and navigate to Mail Flow > Rules. Look for any rules that block ZIP files specifically — for example, rules that trigger on file types with “.zip” or that block potentially harmful attachments. If you find any such rule, you can either edit it to allow ZIPs or disable it entirely.

Review Anti-Malware Policies in Microsoft Defender

Next, check your anti-malware policies in Microsoft Defender for Office 365. Go to the Microsoft 365 Defender portal, then navigate to Email & Collaboration > Policies & Rules > Threat Policies > Anti-malware policies. Open the active policy and look for a feature called Common Attachments Filter. If .zip is listed there, remove it from the blocked extensions list to allow those attachments through.

Consider Data Loss Prevention (DLP) Policies

ZIP attachments can also be blocked by Data Loss Prevention (DLP) policies if your organization uses Microsoft Purview (formerly Compliance Center). Go to compliance.microsoft.com, open the DLP section, and review any active policies. ZIP files might be blocked if they’re suspected of containing sensitive content. If that’s the case, you’ll need to adjust the DLP rules to allow ZIPs or create exceptions for trusted sources.

Use Temporary Workarounds if Needed

If you’re unable to change the policies right away, consider temporary workarounds. You can ask the sender to rename the ZIP file (e.g., change .zip to .zi_) and let the recipient rename it after download. Alternatively, the sender can upload the ZIP file to a cloud storage service like OneDrive, SharePoint, or Google Drive and share a download link instead.

Answer 2

If you are using Exchange Online, ZIP files are not blocked by default, so someone on your end made a deliberate decision to block them. The block itself can be done either via Transport rules (check the Exchange Admin center) or via the anti-malware policy. Check this article for more details.