E-mail Attachments: Blocked File Types

Why are some attachments blocked?

Many worms and viruses spread as attachments to e-mail. As a result, standard practice is to block many of the file types most commonly used by viruses that are not commonly attached to legitimate e-mail. The file types blocked by our servers are listed in a table at the bottom of this page.

What happens to the message if an attachment is blocked?

If the server encounters a file type on it's blocked list or the virus scanner detects a virus in the file,the message is delivered, but the attachment is removed and the message is appended with the following text to warn the recipient:

.zip Files Now Allowed

.zip files were previously included in the blocked list, but advances in our virus scanners now allow us to scan files within .zip archives. This makes the .zip file itself safe to send or receive and is no longer blocked. A .zip file may contain one file or it may be an archive of several or many files. If the .zip file contains a blocked file type or infected file, however, the entire .zip archive will be removed.

Renaming The File Type No Longer Bypasses Filters

The new virus scanning and attachment blocking filters are also able to determine the real file type of an attachment without relying on it's extension name (.zip, .exe, etc.). Previously, if you needed to send or receive a file type that was normally blocked, you could rename the file extension in order to "fool" the attachment removal and allow the file through. Thus you could rename the file "myscript.exe" to "myscript.dog" and send the file through. You would then inform your recipient to rename the file to "myscript.exe" before they tried to open it. This method will no longer work. In order to get legitimate files past the filters, we have an alternate method of using a password protected .zip file.

Working With Password Protected or Encrypted .zip Files to Bypass The Filters

Our filters are unable to scan files within a password protected .zip archive. When the filters encounter a protected .zip file, a warning message is appended to the original message and is passed through with the attachment in tact. If you need to send or receive a file type on the blocked list, you can protect the .zip file with a password and supply the password in your message in order for your recipient to open the file. If you need to receive one of these files, you can forward instructions for your sender to do the same. We have instructions below.

Instructions:

Windows

Macintosh

List of Currently Blocked File Types - updated 8-9-07

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