i was trying to install sendmail with apt-get install sendmail but i got an error that needed some dependencies. so i send this command:

apt-get install rmail

then after it was completed, i was able to send this command again and it worked

apt-get install sendmail

but for some reason i got these two warnings:

on this one i jus said Yes

   If your original static resolver configuration file (/etc/resolv.conf) contains nameserver addresses then those      │
 │ addresses should be listed on "dns-nameservers" lines in /etc/network/interfaces as described in the README. Until   │
 │ you have modified /etc/network/interfaces and reconfigured the affected interfaces resolvconf will not include       │
 │ those addresses in the dynamically generated resolver configuration file. Without those addresses you may have       │
 │ trouble resolving domain names. A TEMPORARY solution is to append the whole original resolver configuration file to  │
 │ the end of the dynamically generated file. This will be done if there is a symbolic link from                        │
 │ /etc/resolvconf/resolv.conf.d/tail to /etc/resolvconf/resolv.conf.d/original. If you agree then this symbolic link   │
 │ will be created, provided that no /etc/resolvconf/resolv.conf.d/tail already exists.                                 │
 │                                                                                                                      │
 │ After you have modified /etc/network/interfaces to add the required "dns-nameservers" lines you should point the     │
 │ /etc/resolvconf/resolv.conf.d/tail symbolic link to /dev/null.                                                       │
 │                                                                                                                      │
 │ Append original file to dynamic file?                                                                                │
 │                                                                                                                      │
 │

on this one i jus said OK

   ─────────────────────────────────────────── Configuring resolvconf    ├──────────────────────────────────────────────┐
  │                                                                                                                     │
  │ Remember to reconfigure network interfaces                                                                          │
  │                                                                                                                     │
  │ Once resolvconf is installed, interface configurers supply nameserver information to it (which it then makes        │
  │ available to the C Library resolver and to DNS caches). However, they do this only when they bring up interfaces.   │
  │ Therefore for resolvconf's nameserver information to be up to date after initial installation it is necessary to    │
  │ reconfigure interfaces -- that is, to take them down and then to bring them up again -- and to restart DNS caches.  │
  │                                                                                                                     │
  │