xa_sharma
You need to properly configure rDNS, DKIM, SPF, and DMARC so that providers (Outlook, Yahoo, among others) recognize your mail server as trusted and don't block your messages.
I recommend using tools like https://mail-tester.com/ or https://dmarcian.com/ to test whether your server meets these requirements.
Of course, this is just the basics, and I can't write a full guide without seeing your actual setup, as it varies quite a bit from server to server.
If you need further help, send over your mail server logs from when you try to send emails and the provider blocks them.