This week’s other mail bomb plot

It’s been barely covered in the U.S. this week, but Greece decided today to temporarily suspend international mail leaving the country after a string of mail bombing attempts: 

 On Monday, several homemade bombs concealed in hollowed-out books arrived in the mail at several embassies in the Greek capital. Another explosive device was discovered addressed to French President Nicolas Sarkozy.

On Tuesday, officials found more parcel bombs bound for embassies in Athens. In the afternoon, the mailroom at the German Chancellery in Berlin was closed after a package bomb addressed to Chancellor Angela Merkel was discovered there. Officials found the explosive device during a routine check and quickly rendered it harmless.

On Tuesday evening, two further packages — one addressed to the European police body Europol and a second bound for the European Court of Justice — were found and destroyed at the Athens airport.

Greek authorities have ruled out al Qaeda involvement and say  the plot is more likely the work of Greek leftist extremists — which often have amazing names like Conspiracy Nuclei of Fire.

Is there enough evidence from this past week to suggest that mail bombing is not a particularly effective form of terrorism in the 21st century?