Invalid format using @localhost

[christianesperar]

Hi! I set up Roundcube on my PC to try it. I successfully set up all the requirements but I have a problem in adding new contacts. For example, I want to add john.doe@localhost as his email since it just on localhost. My problem is Roundcube does not accept this kind of format. I already search on search engine and did not find an answer. Is there anyway to remove the Email Formatting Authentication or I miss something else. Thanks!