Once we forget password on wp login, it provides lost password link that will send email confirmation to owner email, to reset password. The problem is, the link cannot send email because : the mail() function. The notice like this:

The e-mail could not be sent.
Possible reason: your host may have disabled the mail() function.

this mean, on that server, postfix mail is not installed. DO this:

apt-get -y --force-yes -f install postfix

see on screen, and its done. no mail function enabled.

Setting up python-pkg-resources (3.3-1ubuntu1) ...
Setting up tcpd (7.6.q-25) ...
Setting up python-urllib3 (1.7.1-1ubuntu0.1) ...
Setting up python-twisted-bin (13.2.0-1ubuntu1) ...
Processing triggers for initramfs-tools (0.103ubuntu4.2) ...
update-initramfs: Generating /boot/initrd.img-3.11.0-12-generic
Setting up libgtop2-common (2.28.5-2) ...
Setting up wpasupplicant (2.1-0ubuntu1.1) ...
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Setting up python-gdbm (2.7.5-1ubuntu1) ...
Setting up os-prober (1.63ubuntu1) ...
Setting up proftpd-basic (1.3.5~rc3-2.1ubuntu2) ...
 * Starting ftp server proftpd
   ...done.
Setting up apt-show-versions (0.22.3) ...
** initializing cache. This may take a while **
Setting up keyutils (1.5.6-1) ...
Setting up at (3.1.14-1ubuntu1) ...
Setting up python-serial (2.6-1build1) ...
Setting up libwhoopsie0 (0.2.24.6ubuntu1) ...
Setting up x11-common (1:7.7+1ubuntu8.1) ...
 * Setting up X socket directories...
   ...done.
Setting up whoopsie (0.2.24.6ubuntu1) ...
Processing triggers for ureadahead (0.100.0-16) ...
ureadahead will be reprofiled on next reboot
Setting up libcwidget3 (0.5.16-3.5ubuntu1) ...
Setting up screen (4.1.0~20120320gitdb59704-9) ...
Processing triggers for ufw (0.34~rc-0ubuntu2) ...
Setting up apache2 (2.4.7-1ubuntu4.2) ...

Configuration file '/etc/apache2/sites-available/000-default.conf'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** 000-default.conf (Y/I/N/O/D/Z) [default=N] ? dpkg: error processing package apache2 (--configure):
 EOF on stdin at conffile prompt
Setting up libhtml-template-perl (2.95-1) ...
Setting up xz-utils (5.1.1alpha+20120614-2ubuntu2) ...
Setting up ethtool (1:3.13-1) ...
Setting up libgtk-3-bin (3.10.8-0ubuntu1.4) ...
Setting up ncurses-term (5.9+20140118-1ubuntu1) ...
Setting up tmux (1.8-5) ...
Setting up at-spi2-core (2.10.2.is.2.10.1-0ubuntu1) ...
Setting up dbus-x11 (1.6.18-0ubuntu4.3) ...
Setting up python-xapian (1.2.16-2ubuntu1) ...
Setting up python-pam (0.4.2-13.1ubuntu3) ...
Setting up python-twisted-core (13.2.0-1ubuntu1) ...
Setting up gcr (3.10.1-1) ...
Setting up ttf-dejavu-core (2.34-1ubuntu1) ...
Setting up python3-problem-report (2.14.1-0ubuntu3.7) ...
Processing triggers for libc-bin (2.19-0ubuntu6.6) ...
Setting up linux-firmware (1.127.11) ...
Setting up libgphoto2-l10n (2.5.3.1-1ubuntu2.2) ...
Setting up biosdevname (0.4.1-0ubuntu6.1) ...
update-initramfs: deferring update (trigger activated)
Setting up python-openssl (0.13-2ubuntu6) ...
Setting up w3m (0.5.3-15) ...
Setting up installation-report (2.54ubuntu1) ...
Processing triggers for ca-certificates (20141019ubuntu0.14.04.1) ...
Updating certificates in /etc/ssl/certs... 28 added, 12 removed; done.
Running hooks in /etc/ca-certificates/update.d....done.
Setting up mysql-server (5.5.41-0ubuntu0.14.04.1) ...
Setting up ssh-import-id (3.21-0ubuntu1) ...
Setting up policykit-1 (0.105-4ubuntu2.14.04.1) ...
Setting up libecryptfs0 (104-0ubuntu1) ...
Setting up libio-string-perl (1.08-3) ...
Setting up ecryptfs-utils (104-0ubuntu1) ...
Setting up apt-xapian-index (0.45ubuntu4) ...
Setting up colord (1.0.6-1) ...
Setting up accountsservice (0.6.35-0ubuntu7.1) ...
Setting up gnome-keyring (3.10.1-1ubuntu4.2) ...
Installing new version of config file /etc/xdg/autostart/gnome-keyring-gpg.desktop ...
Installing new version of config file /etc/xdg/autostart/gnome-keyring-secrets.desktop ...
Installing new version of config file /etc/xdg/autostart/gnome-keyring-pkcs11.desktop ...
Installing new version of config file /etc/xdg/autostart/gnome-keyring-ssh.desktop ...
Setting up console-setup (1.70ubuntu8) ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-13.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-1.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-4.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-3.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-7.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-2.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-9.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-14.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-15.inc ...
update-initramfs: deferring update (trigger activated)
Setting up unattended-upgrades (0.82.1ubuntu2.1) ...
Installing new version of config file /etc/apt/apt.conf.d/50unattended-upgrades ...
Installing new version of config file /etc/pm/sleep.d/10_unattended-upgrades-hibernate ...
Installing new version of config file /etc/init.d/unattended-upgrades ...
Setting up python3-apport (2.14.1-0ubuntu3.7) ...
Setting up language-selector-common (0.129.3) ...
Installing new version of config file /etc/fonts/conf.avail/69-language-selector-zh-sg.conf ...
Installing new version of config file /etc/fonts/conf.avail/69-language-selector-zh-tw.conf ...
Installing new version of config file /etc/fonts/conf.avail/69-language-selector-zh-mo.conf ...
Installing new version of config file /etc/fonts/conf.avail/69-language-selector-zh-hk.conf ...
Installing new version of config file /etc/fonts/conf.avail/69-language-selector-zh-cn.conf ...
Setting up apport (2.14.1-0ubuntu3.7) ...
Installing new version of config file /etc/apport/crashdb.conf ...
Installing new version of config file /etc/cron.daily/apport ...
Installing new version of config file /etc/init/apport.conf ...
Installing new version of config file /etc/init.d/apport ...
Processing triggers for ureadahead (0.100.0-16) ...
Setting up python3-update-manager (1:0.196.12) ...
Setting up tasksel-data (2.88ubuntu15) ...
Setting up gconf-service-backend (3.2.6-0ubuntu2) ...
Setting up libdevmapper1.02.1:amd64 (2:1.02.77-6ubuntu2) ...
Setting up libdevmapper-event1.02.1:amd64 (2:1.02.77-6ubuntu2) ...
Setting up gconf-service (3.2.6-0ubuntu2) ...
Setting up python3-distupgrade (1:0.220.7) ...
Setting up dmsetup (2:1.02.77-6ubuntu2) ...
update-initramfs: deferring update (trigger activated)
Setting up eject (2.1.5+deb1+cvs20081104-13.1) ...
Setting up gconf2 (3.2.6-0ubuntu2) ...

(gconftool-2:21536): GConf-WARNING **: Client failed to connect to the D-BUS daemon:
Unable to autolaunch a dbus-daemon without a $DISPLAY for X11
Setting up libcryptsetup4 (2:1.6.1-1ubuntu1) ...
Setting up ubuntu-minimal (1.325) ...
Setting up cryptsetup-bin (2:1.6.1-1ubuntu1) ...
Setting up libparted0debian1:amd64 (2.3-19ubuntu1) ...
Setting up lvm2 (2.02.98-6ubuntu2) ...
Installing new version of config file /etc/lvm/lvm.conf ...
update-initramfs: deferring update (trigger activated)
Setting up grub-common (2.02~beta2-9ubuntu1) ...
Installing new version of config file /etc/grub.d/20_linux_xen ...
Installing new version of config file /etc/grub.d/10_linux ...
Installing new version of config file /etc/grub.d/00_header ...
Installing new version of config file /etc/grub.d/05_debian_theme ...
Installing new version of config file /etc/grub.d/30_uefi-firmware ...
Installing new version of config file /etc/grub.d/30_os-prober ...
Installing new version of config file /etc/bash_completion.d/grub ...
Setting up grub-pc-bin (2.02~beta2-9ubuntu1) ...
Setting up tasksel (2.88ubuntu15) ...
Setting up libgksu2-0 (2.0.13~pre1-6ubuntu4) ...
Setting up parted (2.3-19ubuntu1) ...
Setting up ubuntu-release-upgrader-core (1:0.220.7) ...
Installing new version of config file /etc/update-manager/release-upgrades ...
Installing new version of config file /etc/update-motd.d/91-release-upgrade ...
Setting up cryptsetup (2:1.6.1-1ubuntu1) ...
Installing new version of config file /etc/init/cryptdisks-udev.conf ...
Installing new version of config file /etc/init.d/cryptdisks-early ...
Installing new version of config file /etc/init.d/cryptdisks ...
update-initramfs: deferring update (trigger activated)
WARNING: you need to set all of cipher, hash and size for the plain dm-crypt mapping cryptswap1 in /etc/crypttab.
Setting up grub2-common (2.02~beta2-9ubuntu1) ...
Setting up ubuntu-standard (1.325) ...
Setting up update-manager-core (1:0.196.12) ...
Setting up grub-pc (2.02~beta2-9ubuntu1) ...
Installing for i386-pc platform.
Installation finished. No error reported.
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.11.0-12-generic
Found initrd image: /boot/initrd.img-3.11.0-12-generic
Found memtest86+ image: /memtest86+.elf
Found memtest86+ image: /memtest86+.bin
done
Processing triggers for initramfs-tools (0.103ubuntu4.2) ...
update-initramfs: Generating /boot/initrd.img-3.11.0-12-generic
Processing triggers for libc-bin (2.19-0ubuntu6.6) ...
Processing triggers for gconf2 (3.2.6-0ubuntu2) ...
Processing triggers for ureadahead (0.100.0-16) ...
Errors were encountered while processing:
 apache2
Reading package lists...
Building dependency tree...
Reading state information...
The following package was automatically installed and is no longer required:
  ttf-dejavu-core
Use 'apt-get autoremove' to remove it.
Suggested packages:
  procmail postfix-mysql postfix-pgsql postfix-ldap postfix-pcre sasl2-bin
  dovecot-common postfix-cdb mail-reader postfix-doc
The following NEW packages will be installed:
  postfix
0 upgraded, 1 newly installed, 0 to remove and 60 not upgraded.
1 not fully installed or removed.
Need to get 1084 kB of archives.
After this operation, 3609 kB of additional disk space will be used.
Get:1 http://kambing.ui.ac.id/ubuntu/ trusty-updates/main postfix amd64 2.11.0-1ubuntu1 [1084 kB]
Preconfiguring packages ...
Fetched 1084 kB in 5s (210 kB/s)
Selecting previously unselected package postfix.
(Reading database ... 83580 files and directories currently installed.)
Preparing to unpack .../postfix_2.11.0-1ubuntu1_amd64.deb ...
Unpacking postfix (2.11.0-1ubuntu1) ...
Processing triggers for ufw (0.34~rc-0ubuntu2) ...
Processing triggers for ureadahead (0.100.0-16) ...
Processing triggers for man-db (2.6.7.1-1ubuntu1) ...
Setting up apache2 (2.4.7-1ubuntu4.2) ...

Configuration file '/etc/apache2/sites-available/000-default.conf'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** 000-default.conf (Y/I/N/O/D/Z) [default=N] ? Installing new version of config file /etc/apache2/sites-available/000-default.conf ...
Installing new version of config file /etc/apache2/mods-available/access_compat.load ...
Installing new version of config file /etc/apache2/apache2.conf ...
 * Restarting web server apache2
   ...done.
Setting up postfix (2.11.0-1ubuntu1) ...
Adding group `postfix' (GID 118) ...
Done.
Adding system user `postfix' (UID 111) ...
Adding new user `postfix' (UID 111) with group `postfix' ...
Not creating home directory `/var/spool/postfix'.
Creating /etc/postfix/dynamicmaps.cf
Adding tcp map entry to /etc/postfix/dynamicmaps.cf
Adding sqlite map entry to /etc/postfix/dynamicmaps.cf
Adding group `postdrop' (GID 119) ...
Done.
setting myhostname: izul-webserver
setting alias maps
setting alias database
mailname is not a fully qualified domain name.  Not changing /etc/mailname.
setting destinations: izul-webserver, localhost.localdomain, , localhost
setting relayhost: 
setting mynetworks: 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
setting mailbox_size_limit: 0
setting recipient_delimiter: +
setting inet_interfaces: all
setting inet_protocols: all
/etc/aliases does not exist, creating it.
WARNING: /etc/aliases exists, but does not have a root alias.

Postfix is now set up with a default configuration.  If you need to make 
changes, edit
/etc/postfix/main.cf (and others) as needed.  To view Postfix configuration
values, see postconf(1).

After modifying main.cf, be sure to run '/etc/init.d/postfix reload'.

Running newaliases
 * Stopping Postfix Mail Transport Agent postfix
   ...done.
 * Starting Postfix Mail Transport Agent postfix
   ...done.
Processing triggers for ufw (0.34~rc-0ubuntu2) ...
Processing triggers for ureadahead (0.100.0-16) ...
Processing triggers for libc-bin (2.19-0ubuntu6.6) ...

.. install complete.