Do you own the domain "groupware.net"? If not, it's likely that you are trying to relay through a host that doesn't allow unrestricted relay (which is a GOOD THING).
Not sure which mail server you are using, but I use Postfix. In the main.cf of the postfix configuration directory (probably something like /etc/mail/postfix/main.cf) you will either want to change your domain to an IP (if you have no domain registered) or a domain (if you actually have one registered and a DNS service like zoneedit.com that points that domain to your IP).
Your server "savanna" is likely the hostname of the system that is running the email server. It is probably not where the error lies, but it's worth trying to see if that is another server on the network (check /etc/hosts or your DNS server's config).
If you have no idea what I'm talking about anywhere in this email, you may be better off running your email through your ISP's own software. Meaning in your email client you just setup your incoming and outgoing servers as the ones provided by your ISP. Then research how MTA's work, what are available and proceed at that point (Postfix or Sendmail are probably the 2 biggest, followed probably by Qmail).