But you would still have your mail address/endpoint tie to single provider, what's worse that single provider could read/manage all the messages you would pass thru. (mail messages , that's it, would need to compromise client side app to read correctly setup nostr DMs)
Today you can setup your own mail server with few clicks I believe. 
The implicit transport nostr/mail would be nice, although could be little chaotic, like you would give someone out of nostr something that looks like an e-mail, but it's actually nip05 and if the relay wouldn't be able to recieve mail everything just fails apart.