THE FILTER VERBS
Excerpted from the Eudora Help Manual
FOR EUDORA 5.1 and 5.2 (Eudora 5.2 has three additional verbs)

The available verbs for filter matching
in Eudora 5.1 for Windows:
Contains
Doesn't Contain
Is
Is Not
Starts With
Ends With
Appears
Doesn't Appear
Intersects Nickname
Matches Regexp (Case Insensitive)
Matches Regexp
Definitions:
contains or doesn’t contain - If the specified header item
contains or does not contain the text string, filter the message. Other text is allowed to
surround the text string.
is or is not - If the specified header item is or is not an
exact match of the text string, filter the message.
starts with or ends with - If the specified header item starts
with or ends with the text string, filter the message. The starts with item refers to the
first non-whitespace character after the colon, so any spaces after the colon are ignored.
appears or doesn’t appear - If the header item appears or does
not appear in the message, filter the message (the text field is ignored). This is useful for
filtering messages based only on the types of fields they contain. For example, some messages
contain a Reply-To: header, some don’t.
intersects nickname - If the text string is included in a nickname,
whether it is a full address or a nickname within the nickname, filter the message. In other
words, the filter looks in all of your address books for the nickname that appears in the
header of the message. If it finds it, it filters the message accordingly.
matches regexp (case insensitive) (Sponsored and Paid modes only) - If
the specific item matches the regular expressions characters with case insensitivity, filter
those messages.
matches regexp (Sponsored and Paid modes only) - If the specific item
matches the regular expressions characters, filter those messages.
THE FOLLOWING VERBS ARE ONLY AVAILABLE IN EUDORA 5.2
doesn’t intersect nickname - If the text string is not included in a
nickname, whether it is a full address or a nickname within the nickname, filter the message.*
intersects address book - If the text string or nickname is included in
any one of your address books, whether it is a full address or a nickname within the nickname,
filter the message. In other words, the filter looks in all of your address books for all
nicknames. If the nickname that appears in the header of the message is in the address book,
Eudora filters the message accordingly.*
doesn’t intersect address book - If the text string or nickname is not
included in an address book, whether it is a full address or a nickname within the nickname,
filter the message.*
*
In Eudora 5.2.09 Beta, the Intersects Address Book filter verbs seem to
have a bug that requires the email addresses
to be in lower case to match. The 5.2.1 beta appears to have fixed this problem.
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