Backup of an Office 365 mailbox fails with:
Cannot back up the primary mailbox of an Office 365 user: 'error while reading SOAP response'
XML syntax error on line 1: illegal character code <character>: error while reading SOAP response
Acronis software communicates with Exchange Server through Exchange Web Services (EWS). Request and response (SOAP) messages that are sent between the client, Acronis software, and Exchange server are written in XML.
In this case EWS response from Microsoft Exchange returns malformed XML, meaning XML generated by EWS in response to Acronis software request contains characters prohibited in XML 1.0 specification. When Acronis software validates the response against the XML specification, validation fails causing backup failure of the affected mailbox.
Acronis development team is working on the issue. In the next version we will add special logic to handle this scenario.
The issue has been fixed in Acronis Cyber Cloud 8.0, please update to the latest build.