[Mailmunge] Process "outgoing" vs "incoming"

[postfix at ptld.com]

I know technically there is no difference to the MTA between incoming 
and outgoing mail. For this situation im considering messages delivered 
over the submission port and authenticated by SASL login as "outgoing" 
mail.

Is there something built-in to mailmunge like a $ctx->accessor or 
$self->method() to know this difference? Or is passing a SASL macro from 
the MTA using the "-a macro" import the only way?