If Sendmail is not behaving as expected or hangs during installation, it might be because FQDN is not set.
Perform the following steps:
Set an FQDN for your Photon OS machine.
Run the following commands in the order below:
echo $(hostname -f) > /etc/mail/local-host-names cat > /etc/mail/aliases << "EOF" postmaster: root MAILER-DAEMON: root EOF /bin/newaliases cd /etc/mail m4 m4/cf.m4 sendmail.mc > sendmail.cf chmod 700 /var/spool/clientmqueue chown smmsp:smmsp /var/spool/clientmqueue