it would be a very small list. However, the exhaustive list of things other MTAs can do that qmail can't would be huge (starting with backscatter-proof bounces

it would be a very small list. However, the exhaustive list of things other MTAs can do that qmail can't would be huge (starting with backscatter-proof bounces for example) qmail was limited back in the 90ies and it's horribly behind the times now.