Someone tweeted to Matt that PostJoint was penalized.
In fact, if you check out Google for a search on their name, their web site no longer ranks on the first page.
Matt Cutts this morning confirmed it on Twitter saying “any link or guest blog network that claims to have “zero footprints” is waving a giant red flag.”
@techtada any link or guest blog network that claims to have "zero footprints" is waving a giant red flag.
— Matt Cutts (@mattcutts) April 18, 2014
Google recently also penalized My Blog Guest, another large guest blogging network.
I do not see a statement from PostJoint on this penalty yet.
PostJoint, like MyBlogGuest, did talk back to Matt Cutts early on about guest blogging being done. And then after MyBlogGuest was penalized, PostJoint explained how they are different. I guess not different enough?
Postscript: PostJoint responded on their blog saying Matt Cuts Us Out. In short, they are confused about the warning they got but do admit at least 16% of their network received the unnatural links notification. I am not sure how they know that only 16% was hit and not more? Do they have access to all their publishers Webmaster Tools accounts?
So they decide to say “The fact that only 16% of our sites have been hit shows that Google can’t infact trace all of the sites using PostJoint.” Wow.