Often it is necessary to send all outgoing mail via the relay host from the corporate network. This is not so difficult to specify that for Solaris’ sendmail.

cd /usr/lib/mail/cf
vi sendmail.mc

Find this row in sendmail.mc and specify your relay host name or IP instead of relay.sun.com in my example:
define(`confFALLBACK_SMARTHOST', `relay.sun.com')dnl

Then do:
make sendmail.cf
cp sendmail.cf /etc/mail/sendmail.cf
svcadm restart svc:/network/smtp:sendmail

that’s all. To test you can use mailx:
echo "This is the body."| mailx -s "Test subject" mail@mail.com