Incoming mail missing

OS 10.6.8 Mac Mail 4.6 Plusnet POP server

All well for years until two days ago

Incoming mail fine on Plusnet webmail and on Mail on IOS9.1 The same incoming items to Mac Mail are reported as arriving but have no subject nor sender information and are not visible in any folder. They do show up if you "get account info" (without sender or subject).

I have tried turning mail on and off but this has not helped.

Any ideas?