The mailing list for listmasters using Sympa

["José Manuel Bobba Ares" <address@concealed>]

Hello! I want to avoid anyone not being an administrator, or listmaster to post a message from the web interface.
That people can access the interface for configure their accounts, but not post any message to anyone.
I'm looking to the config.tt2 archive for this, but I couldn't find the exact parameter.
Any help will be pleased.
Regards, Jose.