When we migrated from on-premises Microsoft Exchange to Office 365, the default "reply" button in OWA was switched from reply-to-one to "reply all". After the

When we migrated from on-premises Microsoft Exchange to Office 365, the default "reply" button in OWA was switched from reply-to-one to "reply all". After the CEO sent the first all-staff email on the new platform, we had at least three highly regrettable replies copied to the whole organisation, including one disclosing very confidential information intended only for the CEO.