I had noticed that the aminolysis of esters is always shown without an initial protonation step:
It is also drawn the same way in Clayden's 2nd edition page 204.
I could be reading too much into this but I found it strange that this was the case because the reaction between ammonia and aldehydes/ketones to form imines can be acid catalysed, and in that instance the reaction mechanism is always drawn starting with protonation of the carbonyl oxygen, rendering the carbonyl carbon more electrophilic.
How is this reaction carried out in the lab? Is there something preventing acid catalysis? One may be inclined to say acidic conditions may cause the amine to be protonated, making it significantly less nucleophilic. But this isn't a problem for the formation of imines, as long as pH does not dip too low.
Of course, this could be overthinking. But I was just curious if there was something deeper.