Create a new Mail::Filter
object with the given filter subroutines. Each
filter may be either a code reference or the name of a method to call
on the <Mail::Filter> object.
Add the given filters to the end of the filter list.
If the first argument is a Mail::Internet
object, then this object will
be passed through the filter list. If the first argument is a Mail::Folder
object, then each message in turn will be passed through the filter list.
While the filter
method is called with a Mail::Folder
object, these
filter subroutines can call this method to obtain the folder object that is
being processed.
If the filter
method is called with a Mail::Folder
object, then the
filter subroutines may call this method to obtain the message number
of the message that is being processed.