Delayed Attachment Notification and Release


In a 2008 report, enterprise anti virus vendor Sophos reported that approximately 96% of all email is spam. In that same report they also state

"The figures show an alarming rise in the proportion of spam emails sent with malicious attachments between July - September 2008, as well as an increase in spam attacks using social engineering techniques to snare unsuspecting computer users. "

All e-mail messages that pass through the University of Denver's mail transport servers are scanned for viruses. Because viruses and worms passed through e-mail as executable attachments are typically generated automatically and profusely by infected computers, e-mail messages found to contain infected attachments are discarded.

Network security has identified a number of attachment types that have, historically, been used to exploit computer operating system and application vulnerabilities for which software vendors have been slow to release patches. We have chosen to define these as Potentially Malicious Attachments or PMAs.

Because criminals can take advantage of these vulnerabilities in a very short period from the moment they are identified, many institutions block the affected attachment types. The approach at DU is different.

The list of file types considered to be potentially unsafe is given below.


Do not open any e-mail attachment unless you:

  • Know the sender. Do not accept e-mail "candy" from strangers.
  • Confirm that the sender actually sent the attachment. Malicious messages may be disguised as coming from legitimate addresses. Do not open message attachments if you have any reason to suspect the authenticity of the message.


Please review the above warnings before opening any e-mail attachments.

People who need to transmit potentially malicious file types, may do so in several ways:

  • Senders can post the file on a website and tell recipients where they can download it. (This is usually the most appropriate method for distributing files to many recipients.)
  • Senders can rename the file before attaching it and provide recipients with instructions for changing the file name back to its original value.
  • Senders may encrypt the attachment or the message and provide instructions to decrypt it upon receipt.

Important: These techniques are sometimes used by criminals in an attempt to spread malware. The recipient should still heed the WARNINGS given above AND have up-to-date anti virus software installed and working on their system.


E-mail messages containing attachments with the following file types destined for DU e-mail addresses will be delayed when passing through the University of Denver's central mail servers. Because security risks can change rapidly, this list may be modified without notice.

The University of Denver's e-mail servers use the following rules to deal with these file types:

  1. Attachments of e-mails destined for addresses are scanned for viruses. If viruses are found, messages are discarded.
  2. If attachments contain no viruses, messages are sidelined for 4 hours and then scanned again. (The delay is intended to prevent viruses from being distributed before virus signatures are available.) If executable viruses are found in the second scan, messages are discarded. If no viruses are found in the second scan, the messages are passed on unchanged.

Messages will not be rescanned by the mail server. The recipient must take additional measures to ensure the safety of their system and data.


File type



Access Project Extension (Microsoft)



Access Project (Microsoft)



Executable Application



Active Server Page



BASIC Source Code



Batch Processing



Internet Security Certificate File


Compiled HTML Help


DOS CP/M Command File, Command File for Windows NT




Windows Control Panel Extension (Microsoft)


Certificate File


csh Script


Executable File


FoxPro Compiled Source (Microsoft)


Windows Help File


Hypertext Application


Information or Setup File


IIS Internet Communications Settings (Microsoft)


IIS Internet Service Provider Settings (Microsoft)


Internet Document Set, Internation Translation


JavaScript Source Code


JScript Encoded Script File


UNIX Shell Script


Windows Shortcut File


Access Module Shortcut (Microsoft)


Access (Microsoft)


Access Diagram Shortcut (Microsoft)


Access Macro Shortcut (Microsoft)


Access Query Shortcut (Microsoft)


Access Report Shortcut (Microsoft)


Access Stored Procedures (Microsoft)


Access Table Shortcut (Microsoft)


Media Attachment Unit


Access View Shortcut (Microsoft)


Access Data Access Page (Microsoft)


Access Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)


Access Application (Microsoft), MDB Access Database (Microsoft)


Access MDE Database File (Microsoft)


Access Add-in Data (Microsoft)


Access Workgroup Information (Microsoft)


Access Wizard Template (Microsoft)


Microsoft Management Console Snap-in Control File (Microsoft)


Windows Installer File (Microsoft)


Windows Installer Patch


Windows SDK Setup Transform Script


Office Profile Settings File


Visual Test (Microsoft)


Portable Document Format (Adobe)


Windows Program Information File (Microsoft)


Power Point Slide Show (Microsoft)


Power Point Document (Microsoft)


Windows System File


Program File


MS Exchange Address Book File, Outlook Personal Folder File (Microsoft)


RAR archives


Registration Information/Key for W95/98, Registry Data File


Windows Explorer Command


Windows Screen Saver


Windows Script Component, Foxpro Screen (Microsoft)


Windows Shortcut into a Document


Shell Scrap Object File


Temporary File/Folder


Internet Location


VBScript File or Any VisualBasic Source


VBScript Encoded Script File


VBScript Script File, Visual Basic for Applications Script


Visual Studio .NET Binary-based Macro Project (Microsoft)


Visio Stencil (Microsoft)


Visio Template (Microsoft)


Visio Workspace File (Microsoft)


Windows Script File


Windows Script Component


Windows Script File


Windows Script Host Settings File


Excel Document (Microsoft)


Zip Archive


 Ebert squirrel