[snakes1100]

Im shocked that hotmail accepted either emails actually, but again you can blame both ends, the setup is incorrect for postfix, your dns, may also be incorrect, your hostname etc...

Again tho, hotmail claims to have accepted both, technically its not ur issue if hotmail states they accepted them both, it would be easier to fix if hotmail would of rejected them.

Not something that is easily fixed unless your very fluent in Linux and with setting those things above correctly.

Depending how gobabby setup postfix, you will need to edit main.cf and correct anything there, typically /etc/postfix/main.cf

find / -name main.cf -print