Installing PEAR Mail for PHP on Ubuntu is a very simple task. Here is the step by step process how you do it without any delay:
First login to ubuntu server and run below command
sudo apt-get install php-pear
sudo pear channel-discover pear.phpunit.de
sudo pear install -a phpunit/PHPUnit
sudo pear install mail
sudo pear upgrade-all
sudo pear install Net_SMTP
sudo pear install Auth_SASL
sudo pear install mail_mime
sudo apt-get install curl
sudo pecl install xdebug
Source: http://superuser.com/questions/55055/how-to-install-an-updated-version-of-pear-phpunit-on-ubuntu