When I run the installer, there is a step to change some configs, and I use to change de admin password. After this, Zimbra installer saves the options in a log file, and starts the installation. Before press ENTER to save and continue, I have to open other terminal, type "visudo" and include these lines:
Then, save and exit from visudo.
And this must be made in this step. If I do this before run the installer, the installer crazily returns the visudo to "Defaults requiretty" only, removing the next two lines.