Question on SMTP Archiving

Hi All

I haven’t worked with SMTP archiving before and I have a question

I have a customer that is going to be investing in eDiscovery, they understand all Exchange traffic will be captured through Journaling. But they have an internal server that uses  a distribution list which sends email  to a MailMarshall server which then sends these bulk emails to the USA. This process operates outside the Exchange infrastructure.

From reading the SMTP Archiving documentation and looking at the diagram I assume the MailMarshal server is the SMTP relay in the flow of SMTP data so it needs to send a copy of all emails to the Microsoft SMTP Server? EV will then target this.

Is my understanding correct?

Thanks