This can be done without any special integrations on Hive.

1. Use a link to the form hosted off the blockchain Or build an interface around the form. Not a blockchain thing, but can be (ie. dpoll).

2. This can also be done, off-chain. Would require attaining the email addresses, aside from maybe esteem sign-ups (which does not store user emails on chain) not many users are comfortable linking their email addresses directly to a cryptocurrency wallet/account.

A better approach and possibly more helpful email function for the community, since we are not all email marketers and most would simply get annoyed: optional email notifications would work just fine and could possibly achieve what you're reaching for by notifying members of your posts to a specific community.

Cheers