Questions related to attachments


What file types are blocked and cannot be uploaded or sent as attachments?

September 14, 2017

Beginning in August 2017, the Information Security team will be updating our mail filters to block additional potentially dangerous executable file types from reaching University mailboxes. We recognize that this may cause some disruption for email users, however we feel that the risk outweighs the end-user impact. 

Please note that if a file is blocked, the email will still be delivered and that attachment replaced with a text file with the following message "Dangerous file types are blocked for your protection. For any additional questions, please contact the administrator." If the file is required, please contact the CCS Help Centre for assistance (519) 824-4120 x58888 or 

Blocked Attachment File Types

File Extension to Be Blocked

File Type



Windows Executable
Java Source Code
IRC Script File
Windows Installer Package
Program Information File
Windows System File


Currently Blocked

Batch file
Windows Command File
Windows Dynamic Link Library
MS DOS executable
JavaScript File
Jscript Encoded File
Windows Screensaver
Visual Basic File
Visual Basic Encoded Script
Visual Studio Binary
Microsoft Command

Currently Blocked
(As of August 17th 2017)

Currently Blocked
(As of August 31st 2017)
Shell Script
Shell Script
MS Shell
Windows Installer Patch
System File or Shell Script
Program File
Windows Script
Windows Explorer Command
Windows Scriptlet
Currently Blocked (as of September 14th 2017)
What file types are blocked by and cannot be opened by Outlook 2016?

File types blocked by Outlook 2016

Outlook 2016 prevents the opening of attachments with potentially unsafe file extensions by blocking nearly 100 different extensions. When you send an email containing an attachment which has a blocked file extension will receive the following message:

This item contains attachments that are potentially unsafe. Recipients using Microsoft Outlook may not be able to open these attachments. Do you want to send anyway?

Recipients using Microsoft Outlook to read an email which contains an attachment with a file extension that Outlook blocks will see the message that the file has been blocked at the top of the email.

Outlook blocked access to the following potentially unsafe attachments...

The CCS Information Security Team also has a list of file types that are blocked as attachments which may be different than the list of attachments blocked by Outlook.  When in doubt, check the Information Security list. The Information Security team uses a tool called IronPort which checks for and blocks incoming mail messages with a banned attachment.

What is the maximum size file attachment that I can send via email?

The maximum size file attachment that you can send via Gryph Mail is 150 MB.

You should also be aware that although a Gryph Mail user can send and receive attachments of up to 150 MB in size, the recipient's email service can also determine whether delivery of an attachment succeeds or fails.

For example:

Limitations sending or receiving email with Google Gmail:

  • Google Gmail users can receive attachments that are only 50 MB or less in size.
  • Google Gmail users can send attachments of only 25 MB or less in size.