Following on from the excellent advice here:
You may want to add the following:
Without it postfix defaults to smtpd_client_event_limit_exceptions = $mynetworks and won’t apply rate rules to hosts within those networks. So if your problem is internal servers hammering your relay then the limits won’t get applied.
Oh, and if you want to test mail delivery by sending it to the relay host from the command line of one of the other servers:
mail -S smtp 10.1.0.63 -s "Test" firstname.lastname@example.org < some.file.of.stuff