There are many things that direct mail offer that cannot be achieved with e-mail.
Although most direct mail is automated and completely impersonal, it can be adapted in such a way that gives the impression that it is tailored and bespoke.
With direct mail gifts can be enclosed (such as a pen, a diary, a coffee sample etc.). With e-mail a attachment can be sent (with a voucher etc.) but the physical is better than digital.
When receiving something tangible, there is an affect it causes. Humans are physical beings and touching is important; getting something through the letterbox has more effect that in the inbox. Direct vs electronic, maybe direct is better?
As time goes on, more and more of us will get online and more and more business mailings will be done via e-mail rather than post. Generally B2B direct mail is promotional rather than actual communication. However there is still a huge market for direct mail. B2C direct mail is still huge, from pizza shops, insurance companies, water, electricity, tree surgeons etc. will always use direct mail. Your local council still communicates via post. B2B direct mail has dropped off, due to the reduced costs of e-mail it makes more sense for businesses to send information/newsletters, promotions via e-mail rather than by post. It will never truly drop off, but indeed has reduced. Direct vs electronic is a match, both have their uses.