USPS Informed Delivery
Even if you have automated and shifted from physical mail to electronic delivery as much as possible, some important communications still come in hard copy via the postal service.
If you are away from home for a stretch of time and live in the U.S., the United States Postal Service has a nice free feature called Informed Delivery (not available in all zipcodes.) When you sign up, you get an email every morning with an image of the outside of all the envelopes arriving that day along with a listing of any packages being delivered.
Not so exciting when the incoming is junk mail (as in the sample below from my own inbox), but nice to know when a paper check from a client will be arriving.