What is causing SPF softfail in my email (gmail)

Question

This is the original header. Unfortunatelly, I lack skill to properly tackle this issue:

Delivered-To: srdjanbsrdjan@gmail.com
Received: by 10.216.23.133 with SMTP id v5csp102680wev;
        Mon, 30 Sep 2013 14:51:10 -0700 (PDT)
X-Received: by 10.15.67.131 with SMTP id u3mr40332919eex.34.1380577870714;
        Mon, 30 Sep 2013 14:51:10 -0700 (PDT)
Return-Path: <info@dadilja.rs>
Received: from dadilja.rs ([2a01:4f8:d16:1355::2])
        by mx.google.com with ESMTP id l4si2125631eew.41.1969.12.31.16.00.00;
        Mon, 30 Sep 2013 14:51:10 -0700 (PDT)
Received-SPF: softfail (google.com: domain of transitioning info@dadilja.rs does not designate 2a01:4f8:d16:1355::2 as permitted sender) client-ip=2a01:4f8:d16:1355::2;
Authentication-Results: mx.google.com;
       spf=softfail (google.com: domain of transitioning info@dadilja.rs does not designate 2a01:4f8:d16:1355::2 as permitted sender) smtp.mail=info@dadilja.rs;
       dkim=pass header.i=@dadilja.rs
Received: by dadilja.rs (Postfix, from userid 500)
    id D18F2341957; Mon, 30 Sep 2013 23:51:07 +0200 (CEST)
X-DKIM: Sendmail DKIM Filter v2.8.3 dadilja.rs D18F2341957
DKIM-Signature: v=1; a=rsa-sha1; c=simple/simple; d=dadilja.rs; s=default;
    t=1380577867; bh=2AKUNmCuyrAZZl40G8Ws1ED2yu4=; l=2865;
    h=To:Subject:Reply-To:From:Date:Content-Type:
     Content-Transfer-Encoding:MIME-Version:Message-Id;
    b=j6AONYZjHAiwxXq8bRkak+6PXGE2q8Y1yE6XBwIe+SCaSAfavCTna/y4LzNpiCXYk
     NxO/gAFbLXdWqKoFD/rAUIU1vIHn6PyGST04Doqc+Qf9pYxU6QieEStAndCQ6FhDgo
     ua8e2tblmiUcrJgWlrDXsTx/xkpwB2jIlYIzlBuo=
To: =?utf-8?B?c3JkamFuYnNyZGphbg==?= <srdjanbsrdjan@gmail.com>
Subject: =?utf-8?B?S29udGFrdCBvZCByb2RpdGVsamEgbmEgc2FqdHUgRGFkaWxqYS5ycyE=?=
X-PHP-Originating-Script: 500:Sendmail.php
Reply-To: bsrdjan@mailinator.com
From: Dadilja Info <no-reply@dadilja.rs>
Date: Mon, 30 Sep 2013 21:51:07 +0000
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
MIME-Version: 1.0
Message-Id: <20130930215107.D18F2341957@dadilja.rs>

Answer 1

Thing that was causing softfail is that I did not have an entry for IPv6, only for IPv4. I added a TXT entry to my DNS for my IPv6 address, so hopefully, this will fix it