I believe in the code block below from your config file; you will want to change the highlighted portion I made to have useSendmail = false instead of true
$imapServerAddress = 'localhost';
$imapPort = 143;
$useSendmail = true;
$smtpServerAddress = 'mail.oasisone.org';
$smtpPort = 25;
$sendmail_path = '/usr/sbin/sendmail';
$use_authenticated_smtp = false;
$pop_before_smtp = false;
$imap_server_type = 'uw';
$invert_time = false;
$optional_delimiter = 'detect';
Everything else from what I can tell looks ok.
You should be able to run the config script to configure the settings though, makes it a little easier to change, etc.