Why A QSL manager is a volunteer or paid helper, usually located in a country with reliable mail service, who handles the paperwork side of confirming contacts for a DX or DXpedition station. The DX operator sends the manager the log, and the manager receives incoming QSL requests and mails out the confirmation cards. This matters because many rare-entity operators have poor postal service, limited time, or thousands of contacts to confirm for awards like DXCC. Callbook and DX listings print the manager's call as 'QSL via ...' for this reason.
Watch out Running a net so many stations can work a rare DX station describes a DX net control operator, and relaying propagation and pileup information describes a pilot station, neither of which handles cards.
QSL manager = mail clerk. Think 'QSL via W1ABC' in the DX listing: cards, not frequencies or nets.