Emails blocked

I am sending emails using your plugin to people who use a button on the site to request them. The emails go to multiple email addresses. Most are getting through without a problem but ones going to Hotmail and live are having problems. the Hotmail ones do not arrive at all and the Live ones go to junk.
I have spoken to Microsoft who confirm the domain is not blocked and to my host who confirms emails are being sent without any issues.
Is there anything you can help with?
thanks
Bob S

https://wordpress.org/plugins/wp-mail-bank/