Recently I read an article on why polling the community can be counterproductive. Bottom line: it misleads owners into believing that community associations are democracies, and they're not.
No Good Deed Goes Unpunished: The Challenge of Surveying Condo/HOA Owners A quote from a community association attorney:
"Many years ago, I had an association where the board was surveying owners on almost everything the board was deciding," she recalls. "But the board wasn't really clarifying that they were taking surveys.
"They were self-managed, and then at one point, the board decided to hire a management company," says Howard. "The board didn't get the owners ‘vote' to approve that. An owner actually sued, saying the board didn't get approval for that action, and that owner wanted to terminate the management agreement.
"I sort of had to tell that board, ‘You guys set yourself up for this because you let owners think they had a vote on these things,'" she explains. Even if owners don't actually sue the association, it's still annoying to be asked for your opinion all the time, only to see that your opinion has no influence on the board's decisions.
Back to the original question. Mailboxes don't sound like the kind of thing that requires proxies. Use of proxies suggests that this has the same weight as the annual meeting and election - which is one area in which owners do have a say in the outcome. The board needs to clarify why they're doing this, and maybe re-think the wisdom of going down that route.