Hello Chris, 

SmarterMail has a per domain Inbound and Outbound extension blacklist

For the ability to block sending to specific domains, This will be harder to do, The only current way I can see to do this is to use the Spool's command-line options to write a script that will filter the messages.

I will get a feature request added for the ability to control the domain that is being sent to. 

Thank you

Hi Chris,

If you want to prevent the users from sending to ANY domains outside of the server you can turn off the Service Access for individual users or all users on a domain. This is found as the domain admin In Domain Settings > Accounts > edit a user, or Domain Settings > User Defaults (you can also access both as the sys admin).

If they want to allow sending only to specific domains, you can create a custom spam rule but that would apply it to all domains on the server. 

As for blocking specific file types, you can blacklist file extensions for a specific domain in the Domain Settings > General > Attachments card, or for the whole server as the syst admin in Settings > General > Attachments card.

I think want to allow internal email between users and only to approved domains on the outside. Does that make sense?

Another Option.....
If they are having problems with theft, then you might want to allow it to try to catch them, not just block stuff.

(in SM 14 Enterprise.) In the Domain "Events" settings.  You can create an Event that any outbound email that does not match your internal domain, you can crate an action that :
1) adds an additional recipient to the email.  So you could add "SecurityOfficer@yourdomain.com" (not sure if that is CC'd or BCC'd)
or
2) sends a seperate email to "SecurityOfficer@yourdomain.com" notifying them who sent what.

you can also set it to get a notification if they change their forwarding address too.

Declude allows you to create complex rules and apply them to system, domain, or user.   Bring up a copy of SM as an outbound gateway, add Declude, and start configuring and customizing.  The combination can get you to your goal quickly.

 SM is a great mail transfer agent, and Declude is a great mail filtering tool.  The combination is pretty impressive for people who want to control their own destiny.

   I spent 15 years trusting my commercial spam appliance before realizing that their architecture was inadequate to the problem at hand.  Many of the alternative products had similar problems.  Declude was not everything that I wanted out of the box, but it had the right framework, and I could customize it to do what I wanted.  That has made all the difference.