Restriction on IMAP/SMTP run on same server?

[nonplusnl]

Just installed Mailflow and it sure looks promising!
I am self-hosting Exim and Dovecot, and now setting up Mailflow (using the recommended docker installation) on the same server. However, Mailflow does not allow me to set up an account on my mailserver, because "Host resolves to a private or reserved IP address". Which is true, as indeed the mail services run on the very same home-server.

Which leads me to the question: it appears it was a conscious decision to disallow access to localhost. Yet I am sure I am not the only self-hosting hobbyist that runs everything on the same server. What was the reason for the decision, and would it be possible to accommodate my use case?

Thanks!