sendmail supported in Code Igniter, but not postfix or exim

[eluser]bretticus[/eluser]
Unless you specify differently, CI will just use the standard mail() function. As to which binary actually gets called, is determined in your php.ini file. Often it's something like /usr/sbin/sendmail. If your server uses a different MTA, the package installer (Apt or Yum, etc) is smart enough to replace that symlink (they typically are symlinks) to point to it's very own binaries. So you could probably install exim or postfix and this would be transparent to PHP.

Even if you use a config array with 'mailpath' set and you have 'protocol' set to 'sendmail' instead of 'mail', you can still point that variable to the postfix or exim binary paths (which is probably unnecessary still because of the package installer setup I mentioned.)