Blocking External (Spam) email from using internal domain - Exchange 2013

I've read multiple solutions to this problem for exchange 2010/2007 however we're on 2013 and i don't want to try the solutions for 2010/2007. is there a recommended way of doing this for exchange 2013?

the closest solution i've found had no reply:

Solutions for Exchange 2010:
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AmitIT ArchitectCommented:
Better you look for 3rd party solution like Brightmail or MailMarshal. Exchange is not a spam application. So, you won't be able to control it.
masteritlionAuthor Commented:
We have a spam filter on our exchange server (it's an agent) with blocklists' setup, however i know it was possible to block the domain from being sent via an unauthenticated user.

the links i posted above mention this, however not for our version of exchange.

our antispam is eset for exchange.
AmitIT ArchitectCommented:
As I suggested, you keep Exchange separate and SPAM server or appliance separate. Secondly, Spam can be only controlled by regular spam definition update and as an admin you need to regularly create custom rules to block unnecessary emails and mark them as spam.

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masteritlionAuthor Commented:
We decided to implement a spam appliance to mitigate the issues. the appliance checks AD for the proper email address, and blocks external emails from spoofing internal addresses.
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