Files with spam extension are associated with older e-mail clients. It is a junk file.
SPAM file extension - Spam e-mail message
What is spam file? How to open spam files?
File type specification:
The spam file extension is used by older e-mail clients for e-mail message, which is contained spam.
Spam is a junk e-mail often with commercial communication. SPAM is a historical file extension. Not supported and used.