conversation history in “Pidgin Messenger” using Ubuntu

All the messenger logs will be stored under .purple directory located in your home directory.

cd ~/.purple/logs/yahoo/

this is the location where all your yahoo messenger chat logs will be stored.
You can also view the logs by selecting "Conversation -> View Log" when you have the contact window opened.

To send a message to a offline contact, use "Offline Message Emulation". Open "Tool->Plugins" and make sure you have selected "Offline Message Emulation". This will save the message you sent to a offline contact and the message will be delivered once he is online.

If you are offline and a contact sends you a message that will be delivered to you when you come online.

There are other good plugins for pidgin. To install the extra plugins use the command

 sudo apt-get install pidgin-plugin-pack 

source:askubuntu.com