In the last half of the 1980s and into the early 1990s , the Quantum Link online service for Commodore 64 computers offered user-to-user messages between currently connected customers which they called `` On-Line Messages '' ( or OLM for short ) . In the latter half of the 1980s and into the early 1990s , the Quantum Link online service for Commodore 64 computers offered user-to-user messages between currently connected customers , which they called `` On-Line Messages '' ( or OLM for short ) , and later `` FlashMail . ''