Systemd-resolve & Unbound

Hope folk are well, given what’s being going on for the last 2 years.

If systemd-resolve (along with the entries on /etc/resolv.conf) is doing the DNS queries, can I have something like Unbound installed at the same time?

I’m wanting to (or think I should) install Unbound and have SpamAssassin\Postfix use that for it’s DNSBL queries by adding the line in to local.cf etc and have systemd-resolve do everything else.

Systemd-resolve is listening on port 53, so that would mean Unbound would have to listen on a different port number (which it’s manpage says you can set)

Is this doable? Or nuts? [having Unbound & systemd-resolv at the same time]

What’s driving this is in some of the inbound emails, the headers are showing

0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked. See
DnsBlocklists - SPAMASSASSIN - Apache Software Foundation

and reading up on Google says that as the server is using the IPS\Datacentres DNS servers to do the queries to the RBL (along with everyone else) they’re exceeding the 100K lookups so I should use my own local casching nameserver.

Thanks

Dibs

ps. The server is Ubuntu 18 & BIND is not installed.