Google may be cracking down on sites that publish guest posts. There are several reports of unnatural outbound link penalties.

Outbound Link Penalty

An outbound link penalty is a manual action against a website. In this case the publisher relates that Google may have stopped PageRank from flowing from his website.

Guest Post Manual Action from Google

The publisher reported that the manual action email said:

“We have detected that some of your articles are guest posts… We have disabled your authority for your outbound links. Please set your outbound links to nofollow and submit a review request.”