You need to confirm what the MX record address is for your domain. You can do this by going to this site and entering the e-mail domain (the part after the @) for your organization. The MX record address should be the public IP address of your e-mail gateway on your new ISP’s network. If not, contact your DNS provider and have this changed. It could take 24-72 hours for the changes to replicate through the internet. So, you may be without incoming e-mail for quite some time.