Sendmail Fails to Deliver/Receive Mail To/From Remote Users

If your mail domain (commonly the DNS domain) is different from the LDAP domain, you might run into a mail delivering problem. sendmail(1M) derives the mail domain from the domain portion of the hostname returned by gethostname(3N). This means the return address will be in the LDAP domain. Because the mail/DNS domain is different from the LDAP domain, external users cannot respond to the email To fix this problem, change the host entry in the nsswitch.conf file to dns or put dns before ldap.