Newton mailbox will not delete

So I had Newton mail and loved it now they are gone but there mail boxes are still there. Tried to delete them and they just come back and won’t stay in the trash. Deleted them from the apple mail app and loged in to each acc. and tried to delete them that way but they just won’t stay in the trash.

Rather than delete them in the apple mail app I deleted them in the source email app - eg gmail, exchange etc

Tryed to delete them from the source also and they still come back