USPS  fact sheet on expanded access:

Don’t look at the Postal Service and see only brick and mortar Post Offices. Look online at usps.com. Look at mobile devices. Look for Postal Service products at other retail outlets, grocery stores and pharmacies. Look for letter carriers to pick up packages at homes and offices. Look for expanded access to products and services in your neighborhood. Customer needs have changed dramatically. They receive and pay their bills online and communicate by email and text message.

They demand easier, more convenient access to Postal products and services when and where they want them — online, on their smart phones and at the stores they frequent.

• 31,871 Number of postal retail outlets nationwide
• 70,000 Number of other locations to purchase postal products and services nationwide
• 85 Percent of retail transactions that involve purchasing postage stamps
• 14 Percent of retail transactions that involve sending packages
• 35 Percent of postal retail revenue that comes from expanded access locations
• 2,500 Number of Automated Postal Centers (APCs) — self-service kiosks
• 240,000 Average dollar amount generated by each APC in 2010
• 19,000 Number of Post Offices that generated less revenue than an APC in 2010
• 24 Number of hours at usps.com and on iPhone/Droid smart phone postal apps
• 3,800 Number of Postal Service-branded independently managed retail outlets nationwide
• 6,000 Number of Postal Service retail locations that accept passport applications
• 7,200 Number of Walgreens locations to purchase postage stamps
• 3,665 Number of Walmart locations to purchase postage stamps
• 1,130 Number of Office Depot locations to purchase postal products and services
• 600 Number of Sam’s Club locations to purchase postage stamps
• 420 Number of Costco locations to purchase postage stamps
• 600 Number of Staples locations to purchase postage stamps
• 945 Number of Safeway locations to purchase postage stamps

source: USPS