Attempting to create a user with the userid foo via adduser is rejected as being an invalid userid. Userids with @ in them are required for hosting applications where mailboxes for many domains are hosted using dovecot, saslauthd and postfix. A simple patch to accept these ids is attached.
Created attachment 155112 [details] accept @ in userids in shadow-utils
I'm sorry I can't accept this change. usernames should follow POSIX standards or at least some RHEL conventions. You can propose this change on fedora-devel mailing-list and if there is some consensus about it, I'm free to commit the patch.