Why Was My Email Attachment Blocked?

Summary

NCU email blocks attachments of file types often used to spread malware, like programs and scripts. Learn why your attachment was rejected and how to share the file instead.

Body

Sent or expected an email with an attachment, and it bounced or never arrived? North Central University email blocks certain types of files, like programs and scripts, because they're a common way to spread malware. Here's what happens and what to do instead.

What gets blocked

Mostly files that can run or install something on a computer, like programs, installers, and scripts. A few examples: .exe, .msi, .bat, and .vbs. Macro-enabled Word files (.docm) and .rar compressed files are blocked too. Microsoft maintains the list, so it can change.

What happens

If
Then
You send a blocked file
The whole message is rejected and you get an undeliverable message back. See My Email Bounced: What an Undeliverable Message Means.
Someone sends you a blocked file
The message is rejected and the sender gets the bounce. You won't see it. Ask them to share it another way.
You open email in Outlook on the web
Some file types can't be opened or downloaded there, even if the message arrived.

Share the file another way

Don't rename or disguise the file

Changing the file extension or hiding it to get past the block is exactly what malware does. If a file is legitimate, share it with a link instead.

Got an unexpected attachment that did come through? Be careful before you open it. See Safe Downloading: How to Avoid Harmful Files.

Get help

Need to send a file that keeps getting blocked? Submit a request through Microsoft Office 365 E-mail & Calendar.

Still need help? Call the IT Service Desk at 612.343.4170 or visit Miller Hall 226, Monday–Thursday, 7:30 a.m.–9 p.m.; Friday, 7:30 a.m.–4:30 p.m. CT.

Related articles

My Email Bounced: What an Undeliverable Message MeansHow To: Share a File Securely from Teams or OneDriveSafe Downloading: How to Avoid Harmful FilesOutlook at NCU

Details

Details

Article ID: 165466
Created
Wed 10/21/26 9:31 AM
Modified
Wed 10/21/26 9:33 AM
Audience
Employees
Students