Simple Yahoo Messenger Archive Decoder is a Free Software that allows user to read the Yahoo Messenger Archive without having to connect to the internet or without providing the password for that account. No yahoo password needed
This software is not reviewed yet.
Softmarket's YMM (Yahoo Mass Messenger) allows you to send the same message to Yahoo users from a list (just a text file pasted into a text box ). You can use multiple accounts in order to avoid yahoo from blocking your account.