Windows 10 build 10558 (leak)

Microsoft relased on 29th July the Windows 10 for PC devices. As we know, this journey has no end, as Microsoft revealed that will constantly update Windows 10 and the next major update is scheduled for next year, which codename's Redstone. Saying this, the Insider program is running and a couple of builds were released since RTM at 29th July (build number 10240).
Gabriel Aul, on twitter, revealed that no more builds would came out until 6th October, that will be held a conference (Microsoft will talk about Surface 4, Lumia devices (950, 950 XL and 550)) and Band 2, and we can presume a new build coming for Insiders on both platforms - for PCs and phones (build 10559 is flighting to internal Fast Ring).

Thanks to Wzor, we now have access to build 10558 :)
This build was released internally on 28th September and brings some interesting updates. Highlight for Messaging app.
You can download the ISO from Mega, or CloudMail
File name: 10558.0.150928-1738.TH2_RELEASE_CLIENTPRO-CORE_OEMRET_X64FRE_EN-US
Only x64 is available.
(click on pictures to enlarge) 

Messaging app

New registry icon

from http://bit.ly/1KSwpj4