procmail calls to spamc fail with the following AVC:

type=SELINUX_ERR msg=audit(1211644389.204:16280): security_compute_sid:  invalid
context system_u:system_r:spamc_t:s0 for
scontext=system_u:system_r:procmail_t:s0
tcontext=system_u:object_r:spamc_exec_t:s0 tclass=process

domg472 at #fedora-selinux suggested the following policy which fixes the denials.

policy_module(myspamc,1.0.0)
require{ type spamc_t; }
role system_r types spamc_t;

Audit2allow was suggesting role system_r types spamc_exec_t; which didn't work.