Compound condition in custom scrip?

I have a queue which currently emails the queue admin whenever a ticket
is created. What I want to do is have the admin notified if the ticket
is created via correspondence, yet have no such notification if the
ticket was created via the web. I’m envisioning something like this:

On create and not correspond then notify AdminCCs …

I’m sure that something like this is possible with a custom condition
but I can’t find the docs for how to pull it off. Can anyone point me
in the correct direction?