The secondarymx feature seems to behaviour wrongly. If I have a domain in /etc/secondarymx and /etc/remotedomains then email is accepted fine. It looks like the server accepts email for that domain to ANY email addresses and then it re-queues the emails and tries to deliver to the proper server. The issue with this is that spam is accepted at first and then tried to be sent to the proper server. If the proper server rejects it, then the cpanel server tries to bounce it. So the cpanel servers mailq fills up with bounces to non-existent spam addresses. Should it rather behave the same as /etc/staticroutes and try forward it on immediately ?