Conservative exit policies (Reduced-Reduced, which additionally blocks SSH, Telnet, and IRC ports beyond the default) have no statistically significant correlation with IP blacklisting rates or abuse complaint volume. Web-traffic accounts for 98.88% of all connections on Reduced-Reduced exits, confirming that ports 80/443 are the primary abuse vector and that port-restriction does not meaningfully reduce exposure.
From 2017-singh-characterizing — Characterizing the Nature and Dynamics of Tor Exit Blocking
· §5.5
· 2017
· USENIX Security Symposium
Implications
Port-level exit policy restrictions are ineffective at protecting relay reputation — circumvention infrastructure designers should not rely on policy tuning to improve relay longevity or reduce blacklisting.
Structural changes — such as bridge-only architectures, IP rotation, or unlisted infrastructure — are necessary to reduce blacklisting risk, since web-only policies still expose the channels most used for abuse.