Solution: Switched to using Mail::Sender -- it opens a channel directly to the outgoing mail server, so there's no pre-building of anything in RAM, it sends the encoded data immediately. Sweet!

Not sure what the original crash was. Apologies, I should definitely have done some more diligence to be more specific... And I also would bet it was a forehead-slapper. But with a complete revamp of our View::Email to rely on Mail::Sender, it's a non issue now -- all is sparkles and sunshine again.