A spring seal for a cage of a high speed I/O connector, such as those compliant with an OSFP standard. The spring seal suppresses resonances in the operating frequency range of the connector in a space between the cage and a transceiver inserted in a channel of the cage to mate with the I/O connector. The spring seal has multiple peaks, separated by valleys, with short conducting paths between the peaks and valleys. The spring seal may connect a conductive exterior of the transceiver to a wall of the cage, with the peaks contacting a conductive exterior of the transceiver and the valleys contacting walls of the cage. The spring seal may have a plurality of slits that reduce the spring force while providing conducting paths between peaks and valleys.