And...has there ever been a documented case of any sort of viral or disease outbreak caused through mail contact? A quick internet search says no.

By the time a package arrives on your doorstep, it has been through the most awful conditions not conducive to viral survival for days on end, including the postal processing centre overseas, the unpressurised cargo hold of a plane, yet another postal processing centre here, and in the back of a hot delivery van.

The Wuhan coronavirus isn't more resilient than any other virus out there. There are other viruses, diseases etc. that could also be transferred via mail the same as coronavirus, however because the mail process is such a poor vector for virus transmission, we never see mail services being halted to prevent any sort of outbreak.

What's more alarming about the coronavirus is that it spreads whilst the carrier is asymptomatic. The best prevention of viral outbreaks is isolation before the carrier becomes infectious, however people are spreading it person-to-person before they even realise they have it. I'd be less alarmed over parcels and more concerned over the potential lifting of the travel ban from China.