I got this info years back from some now dead site.

Usenet and email message filters consist of the following components:

·A filter expression.
·One of the available kill actions or watch actions.

·A priority between 0 (lowest) and 1000 (highest). Filters are
evaluated in priority order. If more than one filter matches a
message, the highest priority filter's action is performed.
·An optional expiration date, expressed in the number of days the
filter should be kept. Agent automatically deletes expired filters.
This helps you keep the number of filters from getting out of hand.
·An enabled/disabled flag. This allows you to temporarily disable a
filter without deleting it altogether. You can also use the Group
Properties dialogs to temporarily disable all filters for selected
groups.

How to create kill and watch filters

There are two general procedures for creating message filters. You can
determine the one that best applies to what you are trying to
accomplish.

To create a filter based on a message:

1.Select a message.
2.From the Message menu, open the Filters flyout menu.
3.Open the Add Filter dialog box using one of the following equivalent
methods to display the Add Email Filter dialog box:

Toolbar button: for kill filters or for watch filters
Menu command:Add Kill Filter or Add Watch Filter (Filter menu)
Keyboard shortcut:Ctrl+K for kill filters or Ctrl+W for watch filters

4.Complete the settings in the Add Filter dialog box. The Match entry
box is already filled in, based on the currently selected message. For
a description of the settings, see the online help for this dialog
box.

To create a filter from scratch:

If the filter is going to be for a specific group or folder, make sure
the group is highlighted.

1.Select Open Email Filters or Open Usenet Filters from the Window
menu to open the Email or Usenet Filters window (depending on which
type of filter you are creating).

2.Open the Add Filter dialog box using one of the following equivalent
methods to display the Add Email Filter dialog box:

Toolbar button: for kill filters or for watch filters
Menu command:Add Kill Filter or Add Watch Filter
Keyboard shortcut:Ctrl+K for kill filters or Ctrl+W for watch filters

3.Complete the settings in the Add Filter dialog box, as in the
previous procedure. However, in this procedure, the Match field is
blank, requiring the user to enter a filter expression that uses the
valid syntax required.