Random or certain amount of days?

I haven't been on Maple in awhile and I'm in no rush to jump on so I was wondering if those "COME BACK TO US AND WE'LL GIVE YOU A FREE NX THING!" were random or you if it was a certain amount of days you haven't been on that determined which account gets it.

Just something I thought of, I don't know

people even abuse it on mule accs, something like not playing for 2 weeks or something of the sort to trigger it.