[Exim] SMTP conversation during mail forwarding

Could someone enlighten me as to what happens if mail forwarding is set up
like this:

Sender -> Forwarding domain -> Final recipient domain

What I'm curious about is if the SMTP conversation goes something like
this:

HELO "Forwarding domain"
MAIL FROM:<Sender>
RCPT TO:<"Someone@???">

I think it does...? Do some MTAs do it differently, using something else
in MAIL FROM:<> than $Sender?

--
Juha Saarinen