Polls can be created on the web, however for “mailing list mode” users, they cannot vote.
I propose a feature to vote by email. I guess a “simple” way would be to match the first line of any incoming content to the options available. If, for example, the options in the poll were Discourse, Forum, and Example, and the incoming text had on the first line “Discourse”, a vote would be added from that user.
Any additional content could be posted as a standard reply. If there is no additional content, just add the vote. This would also solve the potential problem of emails going out with just the user’s vote, which would therefore no longer be anonymous.