One of the options without using third party tools and sdripts: 1. Use macbook. 2. Open imessage and scroll 1 year back. 3. Export to pdf. 4. Ensure the pdf

One of the options without using third party tools and sdripts: 1. Use macbook. 2. Open imessage and scroll 1 year back. 3. Export to pdf. 4. Ensure the pdf contains 1 year of chatting. 5. Delete all the messages that have just been exported. 6. Repeat above for another year. In the end you will have a pretty looking archive of imessage. Even an old 2013 macbook with 8gb RAM is capable of accomplishing this task.