After reading those articles on, "Great ways to use email marketing for lead generation," it would surely become something that is hard to stomach. It is definitely not a true lead generation tool as it is very much capable of causing spam attacks, whilst the user needs permission to inquire, as it is of a Legal nature in doing so.
The art of getting permission is what lead generation should truly be about, while creating actions from that specific permission is what the lead conversion should entails.
Link: Email Marketing: Lead Generation? Not so much. Lead Con