The IP address Mac sends a message to is 214.255.15.3. An ARIN whois lookup says that address belongs to the DoD Network Information Center (DNIC), which belongs to the US Department of Defense.
Until this episode, viewers didn't know when exactly the Travelers were from but Grace mentions that they're from 431 years in the future which would be the year 2450.
The last show of the series, as it was announced in February 2019 that there would not be a Season 4.
As Marcy is on the bus going home, the street shown is Pemberton Avenue, Vancouver, British Columbia, Canada between addresses 185 and 1331.