Drupal Contact Form - Missing or Disappearing Emails

Linux sendmail sometimes drops emails mysteriously without any error message or log of the written email.

/var/log/maillog will show an entries such as:
Unauthenticated email from xyz.com is not accepted due to [DMARC]

The way to fix this is to have the domain name of the current server in the from field, and the actual from address in the reply-to field.

This can easily be done with Drupal 7 using the contact_reply_to module. Drupal 8 does not require the module.