(These instructions may vary a bit depending on the version of Eudora you use, and the platform—Mac, PC— you use it on)
Select "filters" from the "Windows" menu
Click the "new" button at the bottom of the window, the default name for the filter is "Untitled"---this will change as soon as you set the rule.
On the right side of the screen, check how you wish to filter: Incoming, Outgoing, or Manual
In the 1st "Header" field, type the header you wish to filter on (or select from the popup). The 7 choices are TO:, CC;. FROM:, SUBJECT:, REPLY-TO:; "Any Recipient," "Any header," "Body."
The popup immediately below offers several choices, such as "contains," "does not contain," "is," "is not," and so on---select one. Then type the word(s) into the textbox. Steps 6 & 7 would be used if you are setting up multiple rules for one filter.
[optional] From the next popup ("ignore," "and," "or" "unless") select one of the options
[optional] set up the second set of Header and contents fields
Then, select one or more actions which the filter should take upon finding a message matching your criteria. Initially, all are set to "none." If you select something else, various dialog or text-entry fields will appear.
