Generated email from CRM in NAV is treated spam mail in the customer server


We use CRM module to do Marketing function, we setup to send invitation mail, newsletter mail … about new campaign for new season … . We use Outlook to integrate with Navision to do this. But the email generated from this becomes spam mail in customer email server so they block IP and we can not send anymore. We use company email , using Exchange server mail. We don’t know why how this problem happens? Have anybody faced this problem? How can we solve this?