Hi, Jim! As long as this is just a warning (you can connect and get/send email, you just get a warning about the certificate not matching), you can usually ignore this message. The warning pops up because on Shared (and many Reseller or VPS accounts, depending on the setup), the server's security certificates cover the server name, not the domain name of your email.
If you want to try getting around this, switch the URL you use to your server name URL. Once you have your server name it will be something like biz123.inmotionhosting.com or ecbiz123.inmotionhosting.com . The client will still connect (since your site is hosted on that server) and the certificates will match, so the warning should go away. Hope that helps!