Ready willing and able... leaving exchange...

Our final and last MS servers is and Exchange system. I want to get rid of it... I've been holding out because... Seems like a lot of work. So... Have a system that we designated our new mail server. Installed S71 Pro and sendmail and got all the rpms up to date. We run a Linux DNS for local and internet resolution and all Linux systems pass mail back and forth without any problems. So... Has anyone done a conversion over from exchange? Would like a step by step process so I don't leave anything out and be down for a short period. Kind of a sanity check here.