--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/plugins/virtuser_file/virtuser_file.php	Thu Jan 04 15:50:29 2018 -0500
@@ -0,0 +1,104 @@
+<?php
+
+/**
+ * File based User-to-Email and Email-to-User lookup
+ *
+ * Add it to the plugins list in config.inc.php and set
+ * path to a virtuser table file to resolve user names and e-mail
+ * addresses
+ * $rcmail['virtuser_file'] = '';
+ *
+ * @license GNU GPLv3+
+ * @author Aleksander Machniak
+ */
+class virtuser_file extends rcube_plugin
+{
+    private $file;
+    private $app;
+
+    function init()
+    {
+        $this->app = rcmail::get_instance();
+        $this->file = $this->app->config->get('virtuser_file');
+
+        if ($this->file) {
+            $this->add_hook('user2email', array($this, 'user2email'));
+            $this->add_hook('email2user', array($this, 'email2user'));
+        }
+    }
+
+    /**
+     * User > Email
+     */
+    function user2email($p)
+    {
+        $r = $this->findinvirtual('/\s' . preg_quote($p['user'], '/') . '\s*$/');
+        $result = array();
+
+        for ($i=0; $i<count($r); $i++) {
+            $arr = preg_split('/\s+/', $r[$i]);
+
+            if (count($arr) > 0 && strpos($arr[0], '@')) {
+                $result[] = rcube_utils::idn_to_ascii(trim(str_replace('\\@', '@', $arr[0])));
+
+                if ($p['first']) {
+                    $p['email'] = $result[0];
+                    break;
+                }
+            }
+        }
+
+        $p['email'] = empty($result) ? NULL : $result;
+
+        return $p;
+    }
+
+    /**
+     * Email > User
+     */
+    function email2user($p)
+    {
+        $r = $this->findinvirtual('/^' . preg_quote($p['email'], '/') . '\s/');
+
+        for ($i=0; $i<count($r); $i++) {
+            $arr = preg_split('/\s+/', trim($r[$i]));
+
+            if (count($arr) > 0) {
+                $p['user'] = trim($arr[count($arr)-1]);
+                break;
+            }
+        }
+
+        return $p;
+    }
+
+    /**
+     * Find matches of the given pattern in virtuser file
+     *
+     * @param string Regular expression to search for
+     * @return array Matching entries
+     */
+    private function findinvirtual($pattern)
+    {
+        $result = array();
+        $virtual = null;
+
+        if ($this->file)
+            $virtual = file($this->file);
+
+        if (empty($virtual))
+            return $result;
+
+        // check each line for matches
+        foreach ($virtual as $line) {
+            $line = trim($line);
+            if (empty($line) || $line[0]=='#')
+                continue;
+
+            if (preg_match($pattern, $line))
+                $result[] = $line;
+        }
+
+        return $result;
+    }
+}