what is sensible-mda and do i need it?
Perhaps you've installed sendmail by using the sendmail-bin
individual package instead of installing the sendmail
wrapper package.
Anyway, if you install sensible-mda
(or the sendmail
wrapper package), the problem you're seeing should disappear.
The sensible-* programs are installed so that other system scripts etc. can rely on a program which provides a certain functionality being in the right location.
sensible-mda
is a dependency of sendmail, so it should exist on your system.
Also you should seriously consider not running sendmail.
Either exim4
or postfix
are much better options for real mail servers, and ssmtp
and nullmailer
are much better options for hosts that will only send outbound mail.
As this point the only people who should be running sendmail are those with large old installations or a need for some of the very complex non-SMTP routing that sendmail can do.