Well, maybe it helps to let you know that as soon as your model is too big to be printed, you'll get a quite different message, so that means. Your model is too small,
or contains parts that are too thin to be printed (less than 0.5mm)
I must admitt, that I got error_emails A LOT!
mostly due to holes, size and nonmanifold objects, they do read all different.
And if you read closely you'll find that the information given in the email are pretty much what you need.
Sure they are not specific, they are based on a standard error message.
Sure there is no hint what specific part of your file is not printable.
That would require a person watching the test, and sending the email, to provide proper Information.
Or (what's almost undoable too)
To have a coloured highlight in a screenshot send with the message.
I think they use maybe a set of maybe five to seven different messages:
"too small"
"too big"
"non manifold"
"open vertices"
"wrong normals"
and so on.
It'd be a good idea to know which error leads to wich message, and in what order the file is checked.
So let's say you'll get a message that's because of nonmanifold edges.
Then you know: size is okay, smallest spans are okay, until now no open vertices
And you can add edges to the model to get it manifold.
But:
If you do have a problem with any model that you cannot identify or solve at all,
you can ask in the forum (attaching your model) the team is always there to help,
letting you know what part you'll have to edit.
'sid
ps Don't be too sure about the stl though!
It may pass the upload test, but the actual print-test is a different story
I do have models in my folder that are marked as printable but they are NOT!
(I keep them because the renderings are not smoothed like the new uploads)