cPanel /whm email server configuration

Good afternoon, I wanted to ask for a technical advice, I currently have 2 cPanel whm servers with all the Email Deliverability configuration done. But I'm having a lot of problem with the servers' Email servers, I currently have a thousand cpanel accounts on this server and I have constant bounce of email falling into blacklists like outlook, gmail etc. I wanted to know if there is any solution to this problem examples: use several authenticated ips to output email from the server, use an smtp service for all accounts on the server. I don't know what to do, I just know that I need to solve this urgently, the server is configured for each account to send 300 E-mail per hour I think it's a low value. can anybody help me ?