1. Install the RedHat9.0 system and select the mail server module when installing. 2, after installation, modify the /etc/mail/sendmail.mc file to find daemon_options (`port = SMTP, AddR = 127.0.0.1, name = mta ') DNL modified to daemon_options (` port = SMTP, ADDR = 0.0.0.0, Name = MTA ') DNL
