The validation check for email addresses will not validate an email address that has a TLD larger than 4 characters.
There are TLD's like .foundation and .healthcare that are greater than 4 characters now.
It is a minor issue now but will become a larger problem in the future as more TLD's are created and used.
Effects: "Email address of the server", "Inbox email address", and "Email address" under User Preferences.
Yes, this problem has been reported and it will be fixed in the next release.
Regards,
Michał