If I run the command below, I get after a long time the error message.
command : sa-update --no-gpg

error:
channel: no 'mirrors.updates.spamassassin.org' record found, channel failed

the only thing I can tell is that I can see in my firewall the server tries all the available DNS numbers I have put into the bind9 service, also those of my provider and those of Google.

So somehow it cannot find the mirrors.updates.spamassassin.org

Somebody told me to try this too, but it didn't help :
# perl -MCPAN -e shell

> install IO::Socket::INET6

disable firewall and try to update again.

also check whether your entries in resolv.conf file are correct.

Can you tell me which ports it needs to update? I cannot disable my Watchguard Firewall and I have no other firewall in use on that server.