Microsoft Office Tutorials and References
In Depth Information
Blocked File Types and Exchange
If you use an Exchange account for email, these same file types are blocked by default. However,
the Exchange administrator can modify the list if needed.
Other Attachment Types
Some other file types are not on the blocked list even though they have the potential to carry
viruses. The reason these file types are not blocked is because they are very commonly sent as
attachments. They include Microsoft Word documents (*.DOC), Excel workbooks (*.XLS), and
PowerPoint files (*.PPT). When you receive this kind of file as an attachment, it’s important for you
to be aware of the potential for harm. Even if you have anti-virus software, you cannot be sure it
will catch every virus, particularly because new ones are being created regularly.
The general rule of thumb is to not open any such file unless you trust the source. It is also wise to
have macro security set to a safe level, as described elsewhere in this chapter.
Sending Blocked File Types
Many people have perfectly legitimate reasons for sending blocked file types as attachments. There
are two ways you can get around Outlook’s restrictions to do this:
n Change the file’s extension. For example, if you want to forward a compiled HTML
help file named MyHelp.CHM, change the file extension to something that Outlook will
not block, such as MyHelp.TXT. In your message, instruct the file recipient to change the
file extension back before using the file.
n Put the file in a ZIP or other kind of archive. This kind of file is permitted by Outlook.
You need to instruct the recipient as to how the file can be extracted, of course.
Sending ZIP Files as Attachments
When you create a ZIP file, you have the option of protecting it with a password. Although this
can provide security against unauthorized access to the ZIP file’s contents, it can prevent
antivirus software from checking the ZIP file’s contents for viruses.