It is useful when Docker containers can send e-mail to you in case there is an error condition that needs attention. Here is how to.
Install the sendmail package from your distribution and edit the file /etc/mail/sendmail.mc. Add this line to the end of it:
define('SMART_HOST', '<dns-name-of-your-relay')Done! Just restart sendmail:
/etc/init.d/sendmail stop
/etc/init.d/sendmail start