I keep getting reports of connection refused when the scheduled backup is setup to copy the backup to another server - and it looks like this might be because the firewall is blocking those ports. But, it appears virtualmin is using different ports.
Here are the ports it is trying to connect to from a single email report (where it is trying to back up 8 domains):
Uploading archive to FTP server myusername.mybackupserver.com...
.. upload failed! Failed to connect to my.ip.add.ress:58591 : Connection refused
This doesn’t seem to work - I set the port range to 50000 to 50001, and stopped and started proFTP via webmin, but the virtualmin backup is still trying to use port :63751
That’s only two ports (50000 and 50001). You need any port that might be used for the connection. It can be pretty much any port in that very high range (so, maybe 50000 to 65535).
I haven’t used FTP in 20 years, at least, so I’m not an expert on this. (And, I continue to recommend you use ssh/scp. It’s simpler and historically more secure.)