How do I block emails?

How do I block emails whiich have no subject?

• I keep getting spam emails with pdf Attachment. All the emails have no text in the subject line. Been trying to set a filter to block these but when I leave the subject line blank. Yahoo asks for text? So does anybody know how to block emails that have blank subjects lines ? Thanks in advance.

• Answer:

  If only we could use regular expressions when creating a filter! That would make it easy. But the fact that it's NOT easy to filter such messages is exactly why the spammers use this dirty trick. It's impossible in the free Yahoo! Mail. But I hope somebody will find a way to prove me wrong. In a Yahoo! Mail Plus account, you CAN do it but it's unwieldy, imperfect and will use up 37 of the 50 filters available in the upgraded accounts. Basically the first 36 filters are of this form: If Subject contains "_" Then Move message to Inbox folder, replacing the underscore with a...z and 0...9. So you would have a filter for each letter of the alphabet and each numeral. Then the last filter (and it must be the last) would be like this: If Subject does not contain "a" Then Move message to Trash folder This works because the filters are applied from first to last. All messages with at least one alphanumeric character in the subject line have already been filtered. Any messages that are left necessarily cannot contain an "a" so they are sent to Trash. It's imperfect, though, because a subject line composed solely of non-alphanumeric characters will also be trashed. So if a friend sends a message with a subject line like "?" or ":-)" it will end up in the Trash folder. You could create more of the first type of filter to deal with these characters, but with only 13 filters left you can't cover every case!