Blocking Domains in EHLO Domain Rule
Question asked by Fabio Dias - 8/26/2016 at 4:52 AM
My accounts are receiving a massive amount of spam from these following top level domains:
I noticed that "cloudapp.net" is a big source of spams. Is it safe to block them using a EHLO Domain blocking rule?

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Hi Fabio.  From the domains you've listed, I'm going to guess this is a zero-day attack.  Spammers will purchase a server package from a hosting company that automates domain creation, DNS, and even DKIM signing.  So these emails appear to come from a legitimate mail server.  
MessageSniffer is really good at blocking SnowShoe/Zero-Day spam.  You can start a 30-day trial at Settings >> Activation >> Licensing.
You can also block these at the SMTP level at Security >> Advanced Settings >> SMTP Blocking.  Add a new inbound email address block and enter *.top, *.xyz, etc.
I hope this helps.  

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