IOS – iMessage: How to search for keywords in an individual message thread

I just transferred all my chat history by copying ~/Library/Messages from an existing (OSX 10.8) machine to a new one (OSX 10.10).

Couple of things to note:

1. Quit Messages on both machines before you do this
2. After copying over, delete chat.db-shm and chat.db-wal from ~/Library/Messages on the new machine
3. Empty the Trash. I found that there was a process called 'IMDPersistenceAgent' that was holding on to the files I deleted. I killed that process ( sudo kill -9 pid in a terminal). To find out which process (and the pid) is holding on to those files I used the excellent What's Keeping Me. It found the culprit process, but I wasn't able to kill it from within it (and hence had to resort to killing from a terminal).
4. Start Messages. Now it might seem that you did not get the history back, but you did! Try scrolling up for any existing conversations and you will find that the history has been restored. If you were to start a new conversation with a contact that is not yet visible, you will find the old conversation history is now visible.

I am happy with the above and am not too worried about the list of open conversations not being restored as long as the history itself is there.†w

I had the same problem and I, too, was frustrated as there seems to be no available information on this topic. Not to mention its annoying as hell.

Anyway, this worked for me and it might work for you too.

1. Open Settings
2. Tap "Messages" settings
3. Scroll down to the MMS Email Address.
4. Make sure to enter the MMS Email Address EXACTLY as it is specified with SoftBank. You can find that information if you login to MySoftbank. https://my.softbank.jp/msb/d/top

I actually had this problem when I bought a new iPhone 5. The girl at the shop who set up my phone unbeknownst to me added a space at the end of the MMS email address. Ah well.

Hope this works!