Which of the following relays messages using email addresses based on amateur callsigns?

Winlink (often called the Winlink Global Radio Email system) is a network of amateur radio stations that provides worldwide radio email using radio pathways when standard internet access is unavailable. Users have specific email addresses structured as [callsign]@winlink.org. The other options are digital modes used for live chatting or automated signaling, not email. FT8 is a weak-signal automated mode, PSK31 is for live keyboard chat, and AMTOR is an older teleprinter mode. None of these alternatives use callsign-based email addresses to relay store-and-forward messages.