Not receiving emails when sending with PHPMailer through SMTP auth server

Hello,

I am a PHP developer and my users with hotmail accounts cannot receive any email from my apps such as user registration messages. I am using PHPMailer library with SMTP authenticated connection to a SMTP server. It's only when user has a contact in contacts list with exactly the same Name and email address when there is no problem receiving emails. That's quite bad because at the very first time users do not have my address in their contacts list and thus they cannot receive the first communication.

Also I am having no problem with other email servers such as Gmail or Yahoo. Please, can you give me some advice or solution?

Thank you very much.