I know this has probably been answered but I need to figure this out asap and I couldn't find it.

I need to configure my sendmail server to listen to two Ip addresses. My Isp is changing ip's on me and I'm trying to make all the changes ahead of it so that I don't have any days that email won't come through. I thought the best way to do this was to run the old address and the new address on the server together for a couple days until the dns addresses are finalized if that makes sense. but I can't find any documentation on configuring sendmail to listen on two addresses could some ont tell me how I can do this... thanks

Look in your sendmail.cf for DaemonPortOptions.

I've been there and I have it configured now like this

Daemon_Options('Port=smtp, Addr=63.x.x.x, Name=MTA') in the m4
or
DaemonPortOption=Port=smtp, Addr=63.x.x.x, Name=MTA in the cf

is this the right do I just append the other ip address after the first?

Okay the sendmail.cf now looks like this

DaemonPortOption=Port=smtp, Addr=63.x.x.x 24.x.x.x, Name=MTA in the cf

and it's working but is this right or is it going to blow up on me later?

You could always remove the Addr arguements completely so that it binds to all available.