Where exactly are all my Sent emails stored?

I have an IMAP account (I think) and pay monthly to a service provider for website and email hosting.

My Sent emails seem to only go as far back as 2020.

In the past they used to go back much further than just 2020.

I am wondering how can I see my emails pre-2020? I am looking for an email I sent in 2014, as I need their contact info, which I did not save at the time.

Where exactly are Sent emails stored: on my HD buried somewhere, in iCloud, or with my service provider?

Any help would be very much appreciated.