Aniket P. my quick simple approach to this problem!
Create a multi line field and store the summarise email. Next time when a new email comes in, then add it to the previous summary and then do the further summarising together. That's how you can use that field while working with hubspot's AI.
Other thing you can do is, you can create an integration which stores or picks up last certain emails upon trigger and you can use it. Then by using webhook, just submit it to hubspot workflow and send reply.
