By default, Yahoo Messenger doesn’t save your messages, alerts and conferences but you can enable this feature manually. Click the ‘Preferences’ option in the Yahoo Messenger menu, select ‘Archive’, select ‘Save all my messages’ and after that just hit the ‘OK’ button. That’s all, from now on, a history of all your conversations will be saved.
To view your conversations, just click the ‘Contacts’ menu in Messenger and select ‘Message Archive’. A new window will appear where you can select the desired archive folder that you wish to review.
You can also do this if you double-click the name of the contact you would like to view history from. Then, in the window where you usually see your IM conversations, click Show Recent Messages. If you want to view an earlier conversation, scroll to the top and click View Full Archive.