We were tasked by a customer a year ago to build an in-product email import. All users had Chromebooks and accessed their O365 email within the web experience. Each user was required to individually authenticate and was then able to import emails from their Inbox/Sent Items/Archived/Deleted folders. We also built a background sync process, that could automatically file future responses to that thread.
The framework allowed us to easily replicate with G-Suite for another client.
Let's hope this survey is because Sage are finally going to invest some development resource in this area.
We did script it into a generic Sage CRM component. Apart from our own custom tables to handle the configuration elements, everything else used vanilla Communication and Comm_Link entities and fields.
We only had 1 person working on it in-between other projects. As we had already built the Sage CRM and MS Teams integration, we are able to reuse authentication/token code from that. I reckon it was functional within 3 weeks from concept. Hopefully the Sage Dev's can add something similar to the core offering for everyone.