First of all, you need to understand how your server or domain name ended on MSN block list.
List of reasons:
1. Specific number "spam" or "unwanted" messages from your domain name. We know that you DID NOT send spam, however, recipient can mark your email as "spam" multiple times. This may trigger blocking rules. You should never send any kind of bulk or CC (multi-recipients) or newsletters to following domain names: yahoo.com, outlook.com, live.com, msn.com, hotmail.com, usa.com and aol.com.
2. Invalid SPF record. Please verify Deliverability via cPanel > Email Deliverability. There you can set proper SPF and also DKIM. Email Deliverability Status may show "Valid", but may contain old records which must be removed manually. If you need any assistance, please contact us via helpdesk.
3. Invalid DKIM keys. Once again, you can check them via cPanel > Email Deliverability.
Don't know anything about DKIM? Not a problem! Please contact us for any assistance.
4. Spam event on shared server. It's possible that other compromised account on the same server got involved in major spam event. This may lead to permanent block list. We, your service provider, can resolve this issue via MSN Postmaster Tools. Please open a ticket with complete bounce back message and headers. Email headers are extremely important.
1. You can setup dedicated MX record for your domain names. You won't share your MX IP with anyone: https://billing.westnic.net/order.php?step=0&productGroup=19
Dedicated IP, free setup and 24/7 U.S. based support.
2. Setup secondary, outsourced MX records: https://helpdesk.westnic.net/hc/en-us/articles/360037006634-How-to-protect-your-email-from-outages-and-improve-deliverability (free and paid Google G. Suite options).