How not to get considered "spammer" by hotmail / outlook accounts ?

Hi there !
I'm stuck in this situation: I'm using an OVH email-pro account to send programmatically emails to recipients. Here is the status:
- Gmail: works fine and come in "main" mailbox
- Free: it comes in "commercial"..... it's not that good...
- Hotmail / Outlook / Microsoft: mails come to "spam" ....

Everything is well configured on our side.
I read this link several times:
https://community.ovhcloud.com/community/en/microsoft-hotmail-outlook-live-mail-delivering-problems?id=community_question&sys_id=ff26b548fdde8e902d4c483e6acd51df

But still can't figure out what's wrong.
My attention is on this point:
"After all is correctly setup, you can request your IP to be cleared. That can be done here: https://postmaster.live.com/snds/addnetwork.aspx245"

=> Which IP ? Is the IP of OVH servers ?
In this case, it's strange that OVH IP could be blacklisted ?

BTW, I'm using https://mxtoolbox.com/SuperTool.aspx?action=mx%3aludissimots.fr&run=toolpage
to have a look on my domain, where I can see some OVH IPs:
!image|690x223

For instance, this one: 178.33.252.245.
When I click on Blacklist check, it tells: "We notice you are on a blacklist".

Can you please tell me why OVH IP can be on a blacklist ? And what we can do to clear this balcklist ? If possible ? I think it's OVH jurisdiction to maintain IPs healthy, right ?

Thanks.