I really don't think that there are any more incidents like this in postal facilities than anywhere else. There were several Post Office shootings in close temporal proximity 15 or more years ago and, courtesy of the news media, any violence by a current or former employee of a retail or similar establishment is now called "going postal". Most of these, like the man who went berserk in a Harley dealership here last fall, don't make the national news...it takes something unusual (like the guy with the samurai sword in a German church in April '05) or an attack by a postal employee to get wider coverage.

I haven't heard, BTW, if the lady who supposedly did the shooting was a veteran, with PTSD or otherwise.