Ultimate Goal: To export a massive Yahoo Mail + mailbox with attachments and images to SQL Server

I have a client that has a huge yahoo plus inbox that they are doing away with as they migrate all their operations to the MS 365 Business Premium stack. They have to preserve their historic emails and would like them easily searchable, but this would be a rare occurrence. Emails are dated from present to 2012, so there are hundreds of thousands of emails since this company had all users using this single email account for sending and receiving data. Most of the messages have large image attachments as well.

I would like to migrate all these emails with attachments to a SQL Server Database so that the email content and other flags on emails can be easily searched online and the images retrieved. So, I'm looking for recommendations on best practices or methods when performing a migration like this. I'm thinking about mapping the inbox to outlook via IMAP and then downloading the content from the server to the outlook inbox and then export to PST. From there, I know there are tools for importing PST files to SQL Server, and I'd like recommendation on utilities (especially opens source tools) to aid this process. I also need to ensure that the images and attachements are stored and retrievable from SQL Server as well.

I realize there might be more straight forward methods to achieving my end goal, so I'm hoping others int his community might be willing to share their recommendation or success/failsure stories so I can hopefully go down the optimal path for acheiving this.

Thank you!