But when you’ll try to sign or encrypt the mail with this certificate, Thunderbird will refuse to send the mail as the certificate is not verified.
Your mail certificate is signed by Thawte Personal Freemail Issuing CA certificate, so for verification Thunderbird requires this certificate.
Apparently (at least in my case) Thunderbird doesn’t come with this certificate. So to fix this problem we will have to manually install Thawte certificate.

1. Download Thawte certificates from this page: https://www.thawte.com/roots/index.html and unzip the files
2. Go to Thunderbird “Tools/Options/Advanced/Certificates” and click “View Certificates”
3. Click on “Authorities” tab
4. Click Import
5. Browse to the folder with Thawte certificates and choose “Thawte Personal Root Certificates\Thawte Personal Freemail Issuing CA\ Thawte Personal Freemail Issuing CA.cer” (Just in case I also installed “Thawte Personal Root Certificates\Thawte Personal Freemail CA\ Thawte Personal Freemail CA.cer”)

Now when you click your certificate it should say that the certificate has been verified and you can send your encrypted or signed e-mails

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Feel free ask any questions or leave comments if it was helpful.

So after few unsuccessful installations of Nagios and one successful, I decided to make a short “how to” for installing Nagios on Ubuntu 9.04, which should work 99.9% and hopefully save a lot of time for beginners like me.

1. Install following packages:
sudo apt-get install apache2
sudo apt-get install build-essential
sudo apt-get install libgd2-xpm-dev
sudo apt-get install php5
sudo apt-get install php5-gd

2.  Create and configure required users and groups:
sudo su
useradd -m nagios
passwd nagios
groupadd nagios
usermod -G nagios nagios
groupadd nagcmd
usermod -a -G nagcmd nagios
usermod -a -G nagcmd www-data

3. Download Nagios and Nagios plugins from http://www.nagios.org/download

4. Compile and install Nagios
cd /usr/local/src/
tar xvfz /path/to/nagios-x.x.x.tar.gz
cd nagios-3.1.2
./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-command-group=nagcmd;
make all
make install
make install-init
make install-config
make install-commandmode
5. Set the password for a web-interface login
make install-webconf
htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
/etc/init.d/apache2 reload
6. Install Nagios plugins
cd /usr/local/src/
tar xvfz /path/to/nagios-plugins-1.4.13.tar.gz
cd nagios-plugins-1.4.13/
./configure --with-nagios-user=nagios --with-nagios-group=nagios
make
make install
7. Checks if there are no errors
/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
8. Make nagios to start with system boot:
ln -s /etc/init.d/nagios /etc/rcS.d/S99nagios
/etc/init.d/nagios start
9. Enter the Nagios web-interface by typing
http://localhost/nagios
in browser. Use nagiosadmin and the password you set earlier to log in.

More detailed guide can be found here
Feel free to leave comments if it was helpful or if you have any questions.
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