Who are the primary victims of smurf attacks on the contemporary Internet system?

Smurf attacks were notoriously weaponized against IRC infrastructure - attackers used smurf amplification to flood IRC servers and force users offline, making IRC networks the most prominently affected targets during the height of this attack vector's use.

FTP servers were not the primary targets of smurf attacks; FTP traffic patterns and use cases did not make them the focus of smurf-based flooding campaigns.

SMTP servers handle email relay and were not the characteristic victims associated with smurf attack campaigns.

While mail servers overlap with SMTP, neither category was the well-documented primary target of smurf attacks the way IRC servers were.