The accounts are in my ignore list (Which I don't seem to be able to find at the moment). Maybe a "report as spam" feature which lets users report certain accounts or posts as spam, and once they reach a certain threshold, they can be checked against each other for duplicate links etc.
Just a suggestion and a little frustration, since I really like the external posts feature.
I'll be implementing a fix, probably tomorrow. The short of it is that if enough people ignore an account (in addition to some other activity info), that user will just not show up in the external posts at all. If the same ip keeps doing the same thing, that ip won't show up in external posts.
I'll re-add the ignore list too.