title: ssmtp: 550 invalid DNS MX or A/AAAA resource record
body: <p>I am trying to send a mail from centos machine, but I came to a problem. I have installed &quot;mail&quot; and ssmtp inside my linux machine and I got this response when I try to send a mail.</p>
  <blockquote>
  <p>ssmtp: 550 invalid DNS MX or A/AAAA resource record</p>
  <p>FromLineOverride=YES
  mailhub=smtp.1und1.de:587
  UseSTARTTLS=YES</p>
  </blockquote>
  <p>Of course, with the correct password and user.
  I have tried already couple of users and everybody are returning the same.
  I have tried even with my own user and the password that I have, but it won't work.
  If you have any other approaches to this problem let me know also.</p>
  <p>What am I doing wrong ?</p>