Hotmail and other large email providers are placing very heavy restrictions and regulations on their incoming emails in an attempt to help stem the flow of spam emails.
There are a few things that you can do to help in getting your emails into the intended inbox:
First you can setup postmaster@ and abuse@ email addresses for the main hostname domains on your server. By this I mean set up postmaster@domain.com and abuse@domain.com.
This will show to Hotmail and the others that you are accepting complaints correctly so that if the people do not wish to receive your emails they will be able to do something about it.
You can also have a look at some articles that our team here have written on spam and how to write emails that conform to the rules:
Avoiding the Spam Filters and Other Email Marketing Tips
Improve Your Email Delivery Rates

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