I had the same problem in the past and the solution was to apply for ip whitelisting. Here are the steps for this.
Go to the Hotmail Postmaster website
Click the link " The email I send is blocked or deleted by Hotmail ." You are redirected to the Hotmail Live Problem Finder page .
Review the troubleshooting guide to diagnose the problem. Email from your IP address can be automatically identified as spam for several reasons. Dynamic IP addresses may be used by other parties for spam, or the DNS record for your domain may not appear legitimate for Hotmail servers. Identify and fix issues where your email for Hotmail users will be blocked as unwanted.
Complete the application in the Junk Email Program . This will help Hotmail identify your mail domain and add it to the white list.
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