Is there a way of preventing Students from emailing certian Staff email groups?

[jasoncrcsd]

Maybe Users in the studends OU cannot email them etc

[rdnixon]

Depends on the required group settings. Simplest approach is to only let members post - so just change the group settings.

If you need some non members to post, then use a compliance rule. Block posting to the group at the root level of the org and disable the rule at the OU level of the people who you do want to post. So do an advanced content match for recipient header equals the name of the group for internal sending. 

[BrandonB]

To expound on what @rdnixon stated, here is a rule I have that prevents anyone in allusers from emailing certain groups. If you have a student group, you could use this example:

[robbabiak]

We do something similar to the above.

Conveniently for us our legacy practice is to have "-list" in all of our groups (i.e.  <schoolname>staff-list@example.com, <othergroupname>-list@example.com, etc ) so we have a compliance rule assigned to the student ou bascially dropping anything from student email accounts going to anything with "*-list@example.com" in the address.