Mail Clustering Works! but

Hi All! I have mail clustering enabled for a primary server (Server A) and a secondary server (Server B). Server A went down and everyone failed over and mail routed to Server B as expected (Yea!). However, Server A is up now, but Server B is still getting routed emails and users are still connecting to the secondary server. I read that the clients will connect back to the primary when they are reopened, but when is the clustering funcality going to detect this and start routing mail to Server A once again?

Thanks,