SendMail: Question about changing domain IP

[thebadtheugly]

Forgive my noobness but I am in a real bind and hope someone can point me in the right direction. I need to know how to update the IP associated to the email domain in SendMail. We are moving to a new data provider so I have the new IP range already. I went to the hosting company and updating the mail record and added the IP to the access table in SM but SM doesn't like this and locks up. It won't even boot up properly once the new IP has been put in place; locks up during the MailScanner Incoming check but once I revert the IP change everything works great again. Does anyone know what I could possibly be missing?? Again, apologies for the noob question, our main network guy was let go a few months ago and I am not familiar with SendMail much.

Any help will be great. Thanks.