Recently I asked and also pondered merging my multitude of Posterous accounts.
I asked around and even searched for information, the only answer I found was email help@posterous.com
Since then Richard Mackney (@richardmackney) suggested an idea – in the post options area within a post be it mobile or desktop you can choose which account you post too. This is not the easiest way and I have yet to find an automated/bulk action way to do this, however it does work even if slow.
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