A dsf2 file extension is related to the Delivery Sequence Format (Delivery Sequence File) Second Generation.
DSF2 file extension - Delivery Sequence Format
What is dsf2 file? How to open dsf2 files?
File type specification:
The dsf2 file extension is associated with the Delivery Sequence Format (also known as Delivery Sequence File), a format used by American mailing service to store addresses.
The dsf2 file contains addresses and other information in Delivery Sequence File Second Generation.