Back in July 2012 I discovered a Joomla issue where all mails, sent over a form, were not sent. This only happened in chroot environments using mini_sendmail as mail binary (php value sendmail_path). As Joomla uses phpmailer (another open source project) as embedded mailing system, the issue needed to be fixed in phpmailer. The original article can be found here: Joomla forms (PHPMailer) do not work with mini_sendmail.
The developer and maintainer of phpmailer, Jim Jagielski, made a pretty fast bugfix after I reported the bug, released as version 5.2.2-beta2. But Joomla never took the newer phpmailer version into its libraries.
Now, several months later, things seem to finally move on the Joomla side. As of today, the latest stable version of Joomla is 3.0.3 - and it still uses version 5.2.1 of phpmailer, therefore still containing a non-working phpmailer class for systems running with mini_sendmail. But I just saw that in the github repository of Joomla, the phpmailer class has been updated a month ago to version 5.2.3!
This change contains the very important new parameter which was called a little bit different in 5.2.2-beta2 (it was called $ReallyIsSendmail back then):
+ * Determine if mail() uses a fully sendmail compatible MTA that
+ * supports sendmail's "-oi -f" options
+ * @var boolean
+ public $UseSendmailOptions = true;
This variable, $UseSendmailOptions, must be changed to 'false', when the sendmail binary is mini_sendmail.
According to the commit on github, it looks that the new phpmailer class will go stable in version 3.1. Currently a beta version (Beta4) of 3.1 is available on www.joomla.org and I can confirm it has a newer version of phpmailer embedded (5.2.2). Joomla 3.1 (stable) should be released in a couple of days (it was due in March 2013).