Pull Mail From Other Providers - eviltoast

I’d like to pull mail from other accounts into Proton over IMAP or POP as they arrive.

Proton Mail has a number of articles on importing mail from other providers and for setting up forwarding to their service. This however is less than ideal; I have found all email forwarded from other accounts arrive as coming from myself, instead of the original sender. This is messy and confusing.

Does anyone know of a way to pull mail from other accounts into Proton Mail as or soon after it arrives, while retaining all the original sender information?