There are countries in the world where this would rightly trigger a bomb scare. It's nothing to do with paranoia - in some places mail bombs are a reality.

Which places would that be?

Here is one example: http://en.wikipedia.org/wiki/Miles_Cooper_letter_bomb_campai...

Sadly England seems to be.

http://www.bbc.co.uk/news/uk-england-manchester-23727511

That isn't paranoia.

A rather large bomb was set off by the IRA in 1996 within walking distance of the sorting office in the article. There have been multiple bombs planted recently in NI itself.

NI?

Northern Ireland.