When installing sendmail on Ubuntu these instructions are displayed:
Bash
Creating/Updating SSL(for TLS) information
Creating /etc/mail/tls/starttls.m4...
Creating SSL certificates for sendmail.
*** *** *** WARNING *** WARNING *** WARNING *** WARNING *** *** ***
Everything you need to support STARTTLS (encrypted mail transmission
and user authentication via certificates) is installed and configured
but is NOT being used.
To enable sendmail to use STARTTLS, you need to:
-
Add this line to /etc/mail/sendmail.mc and optionally
to /etc/mail/submit.mc:
include(`/etc/mail/tls/starttls.m4')dnl -
Run sendmailconfig
-
Restart sendmail