This reminded me of a more whimsical old service that used real snails to send email at some indeterminate time. Looks like their home page is still up but it's totally defunct: http://www.realsnailmail.net/ The only message I sent with it (or at least that made it through, maybe I sent more that I don't remember) was initiated in June 2008, at last collected by a snail in May 2011, and the snail Marko delivered it in August 2011.