viruses technically aren't, "Alive," as we know it). Should someone infected with COVID-19 cough on a piece of clothing or mail it will die within a handful of hours or even at the perfect temperature and humidity, last 2 days or so at most. Mail goes through harsh temperatures and gets tossed around. It doesn't sit in a comfy room all day. Your mail will not allow COVID-19 to survive, so you don't need to panic about a package sent from a possible COVID-19 hotspot being infectious. Simply put, it is okay to check your mail.
By the time your mail has arrived any germs from its initial location are generally long since dead. Therefore, if you are avoiding going out as much as possible, you can safely have your preferred comic store mail your comics, to give one example. Should you get a package sent overnight delivery and are still worried, you can always let it sit in your garage or such for an extra day, but you really don't need to worry. Instead, focus on washing your hands and engaging in social distancing as much as possible. Out of all the things to worry about, however, your mail is thankfully not one of them.