Windows 10 PC native mail app - not syncing and duplicates sent email

Windows 10 PC native mail app - not syncing and duplicates sent email

Issue:
I've tidied my emails, but this doesn't seem to be reflected at Zoho's end. I now have different emails online and on my laptop.
I also find that sending emails from my laptop creates two copies, which just clogs up space for everyone.

Background:
I'm using the "Mail" app that comes with Windows 10 (not Outlook). The settings I can see are: download as items arrive; incoming emails on imap.zoho.com:993:1; outgoing emails on smtp.zoho.com:465:1; sync is set to on.
I have the Zoho mail app on my phone and that's syncing OK.

Thanks!