https://www.frankfurt-airport.com/de...and-books.html - This store servers as the post office at Terminal 1. German postal services does outsource a lot of their offices to existing shops. So it is absolutely normal that.
Terminal 1, Bereich A, Ebene 0
Opening times Monday.-Saturday., 08:00-17:00 Sunday., 09:00-17:00

Services available
letter
Send a letter
Buy a stamp
Deliver individual shipments internationally
Submit a PRIO shipment
Submit a security letter internationally
Buy special stamps

parcel
Sending a package
Package pick up
Have the package/return label printed
Drop off returns from participating retailers unpackaged
Issuing notified parcel shipments
Have the package sent to branch/packing station

express
Drop off Express National
Drop off Express International
Issuing notified express shipments

miscellaneous
Perform Postident
Buy a prepaid mobile phone top up
Buy gift and payment cards
Buy a prepaid SIM card Pay with POSTCARD