IP Blocked in spam filters

I use my droplet as email server based in Nethserver from a few years. Now my emails are rejected and I receive this message. Could you help me?

Best regards

This is the mail system at host nethserver.secuware.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                  The mail system

<xxxx@hotmail.com>: host
   hotmail-com.olc.protection.outlook.com[104.47.22.161] said: 550 5.7.1
   Unfortunately, messages from [207.154.196.78] weren't sent. Please contact
   your Internet service provider since part of their network is on our block
   list (S3150). You can also refer your provider to
   http://mail.live.com/mail/troubleshooting.aspx#errors.
   [DB8EUR06FT041.eop-eur06.prod.protection.outlook.com] (in reply to MAIL
   FROM command)
Reporting-MTA: dns; nethserver.xxxx.com
X-Postfix-Queue-ID: C5F3142355
X-Postfix-Sender: rfc822; xxxx@xxxx.com
Arrival-Date: Fri, 29 May 2020 21:07:16 +0200 (CEST)

Final-Recipient: rfc822; xxxx@hotmail.com
Original-Recipient: rfc822;xxxx@hotmail.com
Action: failed
Status: 5.7.1
Remote-MTA: dns; hotmail-com.olc.protection.outlook.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [207.154.196.78]
   weren't sent. Please contact your Internet service provider since part of
   their network is on our block list (S3150). You can also refer your
   provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
   [DB8EUR06FT041.eop-eur06.prod.protection.outlook.com]