When an envoy from Balhae came to Japan in 871, Suenaga, who was the Junior Secretary of the Shikibu-sho (the Ministry of Ceremonial) at that time, was appointed to an attendant for the envoy to welcome them, and he and MIYAKO no Yoshika, who was the Dainaiki (the senior secretary of the Ministry of Central Affairs), undertook this duty.
貞観(日本)13年（871年）に渤海使が来航すると、式部省であった季長はその接待にあたる掌渤海客使に任じられて、大内記都良香とともにこれに対応した。