[exim] Exim4 delay at boot

Hello:

My box runs Devuan Beowulf and within it runs a (VBox) Devuan ascii virtual machine set up
to start up automatically when I boot.

It is not kept on 24/07 but is booted up a few times every 24 hours.

The Devuan ascii virtual machine runs PI-Hole as a recursive DNS server.
It is all working as it should but there's a 'snag in the weave' so to speak:

When booting, I'm getting a (not too) short delay at "Starting MTA:" which is when (as I
understand it) Exim4 does a reverse DNS check.

The problem is that my DNS (unbound) runs on the Devuan ascii virtual machine which I set
up to start up automatically at boot but it is not yet up and running when Exim4 does the
reverse DNS check.

Hence the delay (30/40s?) I am refering to.

Exim4 is set up to receive "local delivery only; not on a network", listens only to IP 127.0.0.1
for incoming SMTP connections and accepts my box's user as the only other destination for
which mail is accepted.

As I am on a wired ADSL connection and have "always on" web access, "Dial-on-Demand"
configuration is disabled.

Is there a way I can avoid the "Starting MTA:" delay at boot?

Thanks in advance,

JHM