[exim] "550 relay not permitted"

Hello!

I can't find my way in the documentation regarding one major issue;
whenever I send mail to test@???, which is just one of my
mailman lists, or even to peleg@???, which should be one of the
main email addresses ("domain.org" is my local domain), I get "host
lists.domain.org [67.18.186.248]: 550 relay not permitted" (in the first
case) or "host mail.domain.org [67.18.186.248]: 550 relay not permitted"
in the second case.

In my configuration file, hostlist relay_from_hosts = MAIN_RELAY_NETS,
and above that: .ifndef MAIN_RELAY_NETS \\ MAIN_RELAY_NETS =
DEBCONFrelay_netsDEBCONF \\ .endif

But, I have read a few things about it in the net, and it seems that
because domain.org is a local domain, the configuration that is relevant
in this case is local_domains.
Though, again in local_domains I have:

.ifndef MAIN_LOCAL_DOMAINS
MAIN_LOCAL_DOMAINS = DEBCONFlocal_domainsDEBCONF
.endif
domainlist local_domains = MAIN_LOCAL_DOMAINS

It's probably something that Debian does as a default.

----

I have searched this list archives, and Debian's docs, and I have found
the following: in Debian's docs, it says: "Please enter a
semicolon-separated list of recipient domains for which
this machine should consider itself the final destination, apart from
the local hostname (${fqdn}) and "localhost". These domains are
commonly called "local domains"." - I didn't know WHERE should I do
that.
But in the archives I have seen that I should edit "dc_other_hostnames"
in update-exim4.conf. I have done that, and added a semi-colon separated
list, with domain.org and lists.domain.org.

After restarting exim, I have tried to send mail again; still, the same
reply.

I'll be happy if you could show me what do I miss.

Thanks ahead!

Peleg.