[lunatic]

How do I properly configure sendmail ? For now, I can send mails, but the domain name is incorrect (it is set to the hostname which
is sparcstation5).

Sending mails to the sparcstation fail. I receive an error mail saying something is not properly configured.

Solaris comes with a standard sendmail. The best way to configure this is usually following a configuration tutorial closely, rather than fixing individual problems.
BTW: there are many reasons not to use sendmail: the common inability to properly configure it without reading a few hundred pages of documentation is one thing; insecurity and bugs, more bugs, and way more bugs are other reasons...