Whitelist mail address invalid

I have 3 mail addresses from the same company that I want to add to the whitelist. TV accepts 2 of them but tells me the third address is invalid. There's no typos or anything. Same thing happens when I try to add 2 of my private gmx.de addresses. Only one of them gets accepted.

I tried this on several different Teamviewer installations (with and without license) with the same result.

Ofc i added the address without the dot at the end that's shown in the screenshot.

I can't even open a support ticket through their website. After entering my license number it just gets stuck loading...