After some search I found that a working table is created during delivery execution (wkDlv_xxx), but I'm wondering whether there is an easy way to access the list of récipients of a delivery, through objects. I tried the 'delivery.broadLogRcp", but at the time of the rule execution this collection is empty.
Can you specify which version of Campaign you are working with? I suspect Classic since you're referring to 'recipients'. Here is the documentation about creating typology rules, including pressure rules for recipients: