Often with Office365 the mail server is fairly restrictive (at least be default) based on feedback we have had from other clients using the service.
Often it will not allow mail to be sent unless it is from the same user that is logging in (firstname.lastname@example.org).
There is an advanced option to address this mail server restriction mentioned in the document along with the other changes to support Office365 and similar services.
Unless they can configure their mail account to allow it to send ‘anonymous’ mail, they should put OverrideSender=Y in the advanced options to force all emails to be from email@example.com.
The attached services document details how to configure advanced options in the config file with examples.
a- Connecting to office 365 usually involves putting in smpt.office365.com for server and 587 for port. Specify an office 365 user and password (both on the email tab in EI).
b- The UseTLS checkbox needs to be set. If it does not show may be in the database only or the CCG email service is not on a version that supports TLS.
c- Last the overridesender=y option needs to be set in the email service configuration file.