Hi,
You can add the following to your user.config file. After changing the user.config, you will have to "touch" the web.config to get IIS to reload both files.
By default, the 10 at the end of the value string is a 9. Increasing it to 10 should allow for TLDs of up to 10 characters. I caution you on increasing it more than you really need to because it can lead to performance issues.
<add key="CustomEmailRegex" value="^([0-9a-zA-Z](['-.\w]*[_0-9a-zA-Z])*@(([0-9a-zA-Z])+([-\w']*[0-9a-zA-Z])*\.)+[a-zA-Z]{2,10})$" />
Thank you,
Joe