I was gumby@MIT-AI.ARPA. By then mail used SMTP but the arpanet had not yet transitioned to IP/TCP. Those .ARPA names were part of a lengthy transition to the

I was gumby@MIT-AI.ARPA. By then mail used SMTP but the arpanet had not yet transitioned to IP/TCP. Those .ARPA names were part of a lengthy transition to the DNS; before this I was just gumby@mit-ai or just gumby@ai The ARPA. TLD isn’t used for hosts any more but has been repurposed mainly for network database lookups. Yes, the `.` after the TLD is there for a reason.