Ignoring authentication, POP and IMAP truly are legacy protocols in the sense that they were designed in an era where bandwidth, not latency was the major constraint for accessing email. It made sense to send a notification that the size of your inbox changed, and let the client decide whether or not to fetch your emails. Since then, internet connections have gotten tens of thousands of times more bandwidth, but the speed of light hasn't improved correspondingly.
Now or then, whatever the bandwidth or latency, why couldn't we just use a REST web service which would let a client access whatever the parameter incl. mailbox size, list the messages, read the messages in form of JSON/XML arrays of metadata + message bodies in Markdown format?
Because without a standard protocol they would be N underspecified proprietary variants: the Gmail web service, the Office 365 web service, the Office 365 from last year web service...
All of them with complicated authentication requirements, idiosyncratic URL construction, and other difficulties. You would throw away the baby and keep the bathwater.
I meant a standardized REST protocol. Why does it have (or ever had) to be something obscure like SMTP/POP3/IMAP if it could be just REST (still standardized, name it whatever)?
There are Google and Microsoft APIs for exactly this. Well not markdown exactly but since emails are not sent in markdown it would be kind of subjective exactly how to properly convert it
