gistfile1.diff

diff --git a/apps/email/js/ext/mailapi/activesync/configurator.js b/apps/email/js/ext/mailapi/activesync/configurator.js
index 38d7a5a..69fe6cb 100644
--- a/apps/email/js/ext/mailapi/activesync/configurator.js
+++ b/apps/email/js/ext/mailapi/activesync/configurator.js
@@ -2931,8 +2931,12 @@ ActiveSyncAccount.prototype = {
         });
       }
       else { // ActiveSync 12.x and lower
+        var encoder = new TextEncoder('UTF-8');
+
+        // On B2G 18, XHRs expect ArrayBuffers and will barf on Uint8Arrays. In
+        // the future, we can remove the last |.buffer| bit below.
         this.conn.postData('SendMail', 'message/rfc822',
-                           mimeBuffer,
+                           encoder.encode(mimeBuffer).buffer,
                            function(aError, aResponse) {
           if (aError) {
             console.error(aError);
diff --git a/apps/email/js/ext/mailapi/composer.js b/apps/email/js/ext/mailapi/composer.js
index f0f8fdd..21917e4 100644
--- a/apps/email/js/ext/mailapi/composer.js
+++ b/apps/email/js/ext/mailapi/composer.js
@@ -3893,12 +3893,22 @@ Composer.prototype = {
    * Request that a body be produced as a single buffer with the given options.
    * Multiple calls to this method can be made and they may overlap.
    *
+   * XXX: Currently, the callback is invoked with a String instead of an
+   * ArrayBuffer/node-like Buffer; consumers that do not use TextEncoder to
+   * produce a utf-8 encoding probably need to and we might want to change this
+   * here.
+   *
    * @args[
    *   @param[opts @dict[
    *     @key[includeBcc Boolean]{
    *       Should we include the BCC data in the headers?
    *     }
    *   ]]
+   *   @param[callback @func[
+   *     @args[
+   *       @param[messageBuffer String]
+   *     ]
+   *   ]]
    * ]
    */
   withMessageBuffer: function(opts, callback) {