Connection: allow custom metadata to be fetched

README.md

@@ -576,6 +576,7 @@ Connection Instance Methods
       * **envelope** - _boolean_ - Fetch the message envelope. **Default:** false
       * **size** - _boolean_ - Fetch the RFC822 size. **Default:** false
       * **modifiers** - _object_ - Fetch modifiers defined by IMAP extensions. **Default:** (none)
+      * **extensions** - _array_ - Fetch custom fields defined by IMAP extensions, e.g. ['X-MAILBOX', 'X-REAL-UID']. **Default:** (none)
       * **bodies** - _mixed_ - A string or Array of strings containing the body part section to fetch. **Default:** (none) Example sections:
 
           * 'HEADER' - The message header

lib/Connection.js

@@ -815,6 +815,11 @@ Connection.prototype._fetch = function(which, uids, options) {
       fetching.push('BODYSTRUCTURE');
     if (options.size)
       fetching.push('RFC822.SIZE');
+    if (Array.isArray(options.extensions)) {
+      options.extensions.forEach(function (extension) {
+        fetching.push(extension.toUpperCase());
+      });
+    }
     cmd += fetching.join(' ');
     if (options.bodies !== undefined) {
       var bodies = options.bodies,