Getting bPost mail from past residents - some a decade past.. some from high volume senders

For privacy, my mailbox and buzzer does not list names. Thus bPost has no way of knowing who lives in the house. So it’s fair enough that they simply deliver everything that matches the address.

I still get mail from someone who has not lived in the house for ~10 years. I also get mail from recently departed residents.

What is my legal obligation? And apart from legal obligation, what is the normal practice?

This is what I have been doing:

① × through the name & address
② write “retourner à l’expéditeur” on the envelope
③ circle the return address
④ drop it in a red bPost box

I read that in some countries it’s illegal to write on envelopes on the off chance that ink bleeds through or a hard strike of a ball point pen damages the document inside (which could be a birth certificate). What’s the expectation in Belgium?

One utility company is relentless with repeatedly sending mail to a past resident. I’ve returned ~20 or so envelopes and they are not getting message.

In one uncommon case, an envelope arrived for a past resident with no return address. What happens with that?