Hi! I've installed the Courier mail server. Well, I compiled it, satisfying the dependencies on the way. I made it start. I even made the authdaemon start. But, when I try to send an email, I get these errors: "Address family not supported by protocol" and "DNS lookup failure". My host is perfectly visible from the inside AND from the outside by using DNS lookups. Do you have any ideas about my problem? Thanks. By the way: my GNU/Linux is Slackware 10.1

Did you check out /etc/resolv.conf?
This file dictates how hostnames are looked up (eg via DNS, LDAP, etc).

Edit: on the machine itself, you may want to try a few DNS lookups (eg via
the deprecated "nslookup" command or via "dig"). Just to make sure DNS is correctly
set up on the machine itself.

Yes. I did that. I checked both of them. Everything just works. nslookup gives me the correct address, so does dig. /etc/resolv.conf just looks fine. I tried lots of configurations of it and it works. Have no idea what is going on... Maybe a socket error...

Have you tried to do:
telnet <your_mail_server> <SMTP port>
(I think the SMTP port's number is 25, but I'm not sure).

If that works, the sockets/connections should be OK (ie no firewall in the way).

As for "Address family not supported by protocol", have you verified:
-The protocols that your mail server supports/is configured for?
On the Courier Mail server website, it sais that ESMTP, IMAP and POP are supported. Are you
sure you're using the right protocol?
-The e-mail address you're using? Start for instance by sending a mail from your mailserver to a local user.
Perhaps, you could have a look at the maillog to know what went wrong.
Try multiple forms of the e-mail address: eg just "user", "user@your_domain", "user@localhost.your_domain",
etc.
-Are the mail aliases and stuff correctly set up?

Thanx for suggestions . I found the problem: the mandatory thing was the IPv6 support. I don't know why, they didn't write in the README that was a mandatory thing... Well, I'm glad it works . Thanx again for your help

No problem. That's why you used this forum in the first place, no?
You might want to close this thread now.