Thank you for answering me! 

I've just followed some guides for customizing Ircd Hybrid config (on Raspberry
Pi), and usually they suggest to include an encrypted password authentication
for any user, as per the related Ircd config section:

auth {
user = "*@*";
class = "users";
flags = need_password;
encrypted = yes;
password = "PASSWORD_FROM_mkpasswd";
};

Maybe I just have to consider to remove this if I want to allow joining from
the BBS.

Thanks!
--- SBBSecho 3.20-Linux