Do you have API for client messages

Do you have an API to access the messaging to/from clients, could this be done ?

You can use the API to quickly pull a list of all client names and emails. You could then pump that into a third party app like MailChimp for designing custom emails and dispatching to all clients.

I found this API, can i use it to send messages between companies working as a group within Quickfile ?

<System_AccountQuery  xmlns="http://www.QuickFile.co.uk"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  xsi:schemaLocation="http://www.QuickFile.co.uk http://www.quickfile.co.uk/WebServices/API/Schemas/invoices/System_AccountQuery.xsd">
    <Body>
        <LoginCredentials>
                <Email><![CDATA[test@email.com]]></Email>
                <Password><![CDATA[1234567890]]></Password>
        </LoginCredentials>
    </Body>
</System_AccountQuery>

No, this will just return some meta data for an account. It has no means to send messages between companies.