According to progressive direct mail guru Mal Warwick,
Meanwhile, according to academic researchers who study electoral campaigns, direct mail has negligible effects on voter turnout.
Maybe it's persuasive -- that is, instead of influencing whether people vote, it influences who they vote for? Apparently not. For example, according to a tightly designed study in a hotly contested primary that turned on a nasty "wedge" issue (abortion), direct mail only helped the pro-choice candidate when coupled with intensive phone contacts.
So what is direct mail good for? Perhaps for making profits for mail "experts" and fundraisers? This seems to be a campaign method whose time has come -- and gone.