Check your /etc/postfix/main.cf
Do you have
smtp_generic_maps = hash:/etc/postfix/generic
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options =
smtp_use_tls = yes
smtp_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt
relayhost = smtp.office365.com:587
myhostname = yourhostname.WhatEverItIs.com
mydomain = yourhostname.WhatEverItIs.com
myorigin = yourhostname.WhatEverItIs.com
The Commercial System Admin module should set this for you if you used the recommendations in my other post: