Dont know if this is possible, but:
I have several Mautic installations.
They all send emails from one external SMTP server.
If I send an email from Mautic A (that sits on Server A) and send an email from Mautic B (that sits on Server B) there will be a difference in the header (my SMTP provider adds a header with received from and the servers IP address, which I think is standard).
Is there anyway to fake this? So I only send info from Server A.