Discourse operates essentially in the same way as Mailman 2 with from_is_list = Munge From – with those settings every Mailman list email is “From: email@example.com” (rather than “From: firstname.lastname@example.org”) – and similarly every email notification from Discourse is from the same forum email address (email@example.com or whatever).
But I wasn’t really asking about replicating the feature in Discourse. [Edit - as you have realised - I’ve just seen your second reply!]
I was meaning: when this Mailman setting is on, would your script import these messages as being from a single Discourse user (whose email address is firstname.lastname@example.org), or would it instead be able to identify the original sender?
Hope that makes sense!