In Mail big delay in showing email content

Its been doing this for a little while now but - on the left pane of Mail I can see emails are waiting to be viewed, on the right side I can normally see the content of that mail but its blank except for the header. It takes ages for that to populate. In an emergency I can elect to forward the selected email and it immediately shows me the content as part of the forwarding process (but of course it doesnt let you use any hyperlinks in a forwarded mail)

It eventually does populate, but that can take 30 minutes easily. This has been happening for the last few months with my workaround for emergencys. I'm running Monterey on a 2016 27" Mac