When using O365 mail server in confluence, the support ticket creation fails.
This is because the from address in the email header is replaced by the 'Contact email' form field.
Due to security reasons, O365 disallows emails being sent where the from address and username do not match. This can't be changed in O365.
Therefore the 'Contact email' field needs to go into the email header 'Reply To' field and not the 'from' email header field.