Hotmail not receiving newsletters

hello everyone,

First off thank you for your time.

I am sending out newsletters to our 3,000 subscribers. About 20% of these are hotmail users but our newsletter is getting rejected by hotmail. None of them get it at all. We get the email returned from postmaster@hotmail.com saying delivery failed to these recipients.

My question is...
Is there a correct way that the html coding should be to avoid this? Or something that I should add to the code? Or a server configuration issue?

I just want to know how to have my hotmail users get their newsletter. They are upset they don't get it.

Is there a template or tips you can share as to the coding of the newsletter? If that's the case of course. I just can't figure out why only hotmail rejects it.

Please help!

I use Simple news with mimemail if that makes any difference.

Thank you in advance.