Whitelist invalid mailaddress

I'm trying to whitelist 3 mail addresses from the same company. 2 of those addresses get accepted but when I'm trying to add the third address i get the following error telling me the address is invalid.

https://picload.org/view/dgdgpwww/teamviewer1.png.html

I tried adding the address to another Teamviewer Installation and got the same error. There is no typo or anything. I didn't type in the dot at the end that shows up in the picture.

Teamviewer Version is 12.0.83369