I have a single Exchange 2013 server on which I've enabled the AntiSpam filters.  I'd like to configure a rule to block .zip files, but I can't find documentation on this anywhere.  Is this possible in Exchange 2013?

You can do that with a transport rule.

Hi Greg,

Agree with Ed Crowley's suggestion. You can new a transport rule to block the .zip files on EAC or EMS.

What's more, before you create or modify Transport rules in your production environment, we recommend that you use a test environment to understand the effects of the rule, or use the rule in test mode. Test all rules before creating them in a production environment.

Here are some threads about transport rules for your reference.

Transport Rule Predicates

http://technet.microsoft.com/en-us/library/jj919235(v=exchg.150).aspx

Manage Transport Rules

http://technet.microsoft.com/en-us/library/jj657505(v=exchg.150).aspx

Block specific type file in attachment, Exchange Server 2010

http://social.technet.microsoft.com/Forums/en-US/d0c1b19e-4a4d-4c58-a22d-2ca4c54b35ff/block-specific-type-file-in-attachment-exchange-server-2010?forum=exchangesvrsecuremessaginglegacy

Hope it helps.

Best regards,
Amy