This plugins uses PHP imap_open to test if a connection can be established. Roundcube uses socket connections. So either PHP imap module is not available or the imap_open_flag ...
PHP Code:
/* imap_open flag (http://php.net/manual/en/function.imap-open.php) */
$rcmail_config['imap_open_flag'] = 'novalidate-cert';
... is misconfigered in the plugin configuration.
As a workaround you could disable the connection test in accounts.php:
PHP Code:
function test_connection($username,$password,$imap_host,$imap_port,$prot){
add here:
PHP Code:
if(function_exists("imap_open")){
$rcmail = rcmail::get_instance();
$flag = $rcmail->config->get('imap_open_flag');
if($flag)
$this->imap_open_flag = $flag;
$password = $rcmail->decrypt($password);
if($prot){
$imap_open = "{" . $imap_host . ":" . $imap_port . "/imap/" . $prot . "/" . $this->imap_open_flag . "}INBOX";
}
else{
$imap_open = "{" . $imap_host . ":" . $imap_port . "/" . $this->imap_open_flag . "}INBOX";
}
if($res = @imap_open($imap_open, $username, $password)){
$success = true;
imap_close($res);
}
else{
$success = false;
}
}
else{
$success = true;
}
return $success;
}
(PHP: imap_open - Manual).