Filtering emails as per documentation

I believe that “custom scripts” is the right place to ask the question.

I’d like to use the feature of condition as documented Email Account … but the “Condition” box does not seem to be available.

Is there something specific I need to activate to use this aspect?

My end use for this will be to have one inbox@[domain] that collects emails for support@; invoicing@; etc. as to not spend and manage extra email accounts.