Years ago Yahoo would go thru phases where it would decide that TML was a spam source, esp when a whole bunch of msgs would come at the same time.
For the last few years it's only the occasional msg that winds up in the spam folder.
However, in my experience, this problem is NOT exclusive to TML.
I learned years & years ago, even before I had Yahoo & used the various services my employer supplied, that the spam folder MUST be checked each & every day unless one really doesn't care if something really, really, important winds up in there, cuz' eventually that's exactly what will happen.