[MlMt] Clicking doesn't mark "Read"

[Dave C]

It used to be the case that if I clicked on a message in the Message 
Viewer window it would automatically be marked as “Read”. This is no 
longer the case: clicking on it changes nothing.

I don’t see this option and where to set it. Where is this setting?

Thanks,
Dave
Mailmate 1.12.4
Mac OS 10.12.6 Sierra