Perhaps the link below will help. There are herbarium specimens on at least some of the links.

Here is a link that might be useful: Eflora taxon Madagascar

It looks like a kind of Albizia to me , Albizia lebbeck?

Many thanks to you all! No, unfortunately it is not an Albizia lebbeck. I searched in Eflora taxon Madagascar without finding anything convincing...
Maybe it is a subspecies of Acacia nilitica ...

Can't contribute to any information, but - Nice photo series, very carefully showed us what we needed to know.

brunob, I sent you a private message through Gardenweb. I hope you received it. It contains the name and email of an expert who should be able to give you a valid name.

Many many thanks Caro23 for your previous link and for the email address that you sent me. Certainly I will try to submit the topic to the expert that you have suggested. As soon as I get an answer I'll make you know. Best regards, Bruno

Sometimes messages fail to go through Gardenweb so I thought I would verify that.
Looking forward to learning the name .....
Carol

Hi,

Any chance I could send you some postage money to send me some seed pods if you have any to spare.
I also have a trade list, but its not that impressive. If you see something there that interests you that's fine too. I really, really like that acacia,whatever it might be.
Send me an email if its doable.
I usually don't ask except in the trade forum, but I didn't want to chance a missed opportunity.
Don't feel obliged, If you rather not that's fine,no hurt feelings.

This looks like a Pithecellobium to me, but I don't recognize the fruit so I don't know the species.

Carol23: still no response by the expert