RFC 882, which defined domain-style addressing, was released in 1983: https://tools.ietf.org/html/rfc882 There was domain-style addressing that predated domains like ".com" and ".edu". The original top-level domains were ".arpa" (for ARPANET) and ".mil" (for MILNET). Symbolics was "symbolics.arpa" before it was "symbolics.com".
If anyone knows: How were RFCs distributed before the modern Internet as we know it existed?
DISTRIBUTION
One copy only will be sent from the author's site to"
1. Bob Kahn, BB&N
2. Larry Roberts, ARPA
3. Steve Carr, UCLA
4. Jeff Rulifson, UTAH
5. Ron Stoughton, UCSB
6. Steve Crocker, UCLA
Reproduction if desired may be handled locally.
https://www.rfc-editor.org/rfc/rfc3.html