Function to test most of the possible options of a connection:
function imapConfig($options, $i=0, $till = array()) {
 if(sizeof($options)==$i)
 return $till;
 
 if(sizeof($till)==0)
 $till[] = '';
 
 $opt = $options[$i];
 $new = array();
 foreach($till as $t) {
 foreach($opt as $o) {
 if(strlen($o)==0)
 $new[] = $t;
 else
 $new[] = $t.'/'.$o;
 }
 }
 return imapConfig($options, $i+1, $new);
 }
function imap_test($server, $port, $dir, $username, $passw) {
 $options = array();
 //$options[] = array('debug');
 $options[] = array('imap', 'imap2', 'imap2bis', 'imap4', 'imap4rev1', 'pop3'); //nntp
 $options[] = array('', 'norsh');
 $options[] = array('', 'ssl');
 $options[] = array('', 'validate-cert', 'novalidate-cert');
 $options[] = array('', 'tls', 'notls');
 
 $configOptions = imapConfig($options);
 foreach($configOptions as $c) {
 $mbox = @imap_open("{".$server.":".$port.$c."}".$dir, $username, $passw);
 echo "<b>{".$server.":".$port.$c."}".$dir."</b> ... ";
 if (false !== $mbox) {
 echo '<span style="color: green"> success</span>';
 }
 else {
 echo '<span style="color: red"> failed</span>';
 }
 echo '<br>';
 }
 }
imap_test('mail.server.de', 143, 'INBOX', 'username', 'pwd');