sendmail mqueue-client folder snowballs

i noticed a huge spike in disk IO every 22 minutes, and over time, the average disk IO was trending upwards linearly. i found out this is due to a cron job being run for sendmail to clear out the mail queues. however, stuff wasn't getting cleared out and instead was snowballing.

i currently have 13000+ files sitting in /var/spool/mqueue-client. these files indicate snowballing failures in sending a message. the original message was from smmsp (the mailer daemon) to root@localhost to report a failure in mime8to7. when that failed, the mailer daemon wanted to send a message back to smmsp to note that the delivery had failed. when that failed, it tried to send a message to postmaster. from there on, it kept trying to send stuff back and forth to indicate a message had failed delivery.

why didn't sendmail stop trying to send these messages? i want sendmail to drop any message on the floor when it sees a recipient it doesn't recognize. how do i configure this?