We head that Posterous.com is closing on April 30, 2013. Some free services are not meant to last forever. Anyway, here's some info about websites that will "last forever."
You can transfer the content of your Posterous.com free blogs to PostHaven.com (5 dollars a month)
We wish Garry Tan and Brett Gibson (two of the cofounders of Posterous in 2008) all the best.