SQD file extension - Squish message base file format
What is sqd file? How to open sqd files?
File type specification:
The SQD file extension is also related to Squish program and used for its default message format. Squish is both the name of a FidoNet mail tossing application originally designed for DOS and OS/2, and the name of the primary mail storage format in which this application stores. Most likely old and no longer used format.