I do recognize that IMAP is not as rich a data source as GMails API, but I'd encourage you to not feel limited by that. I don't mind using hosted email, as long as the revenue source is coming from my wallet, rather than ads.
I even had spec'd out building an OSS self-hosted server that ingested email via IMAP and then stored metadata in its own database - this had the benefit of being as rich as GMail APIs, but me as a user still getting to own my data.