title: Send mail with sendmail to gmail
body: <p>I have a server on OVH and I'm trying to send some mail to my Gmail address using sendmail.
  I installed sendmail with apt-get on debian, and <code>echo "Subject: test" | /usr/sbin/sendmail -v mymail@gmail.com</code> works. However Gmail puts the mail in the spam folder and says the mail is not authenticated.
  I have no knowledge of how email works and from what I've seen I could use SPF or DKIM to provide authentication, but it seems it requires admin access to ovh DNS servers. 
  What would be the easiest way, using only admin access to the server that sends mails, to make sure emails sent from it are not marked as spam ?</p>
  
  <p>Thanks</p>