My provider has decided to switch off the default port 22 for SSH and bind it to a port above 1024.
I assume this is the relevant line I need to change in nt_export_djb.pl:
"$rsync_path -az -e ssh data.cdb tinydns\@$rhost:$ns->{'datadir'}/data.cdb"
I'm just clueless as to how to change it correctly.
Never mind, I think I fixed it:
Rsync accepts the following argument -e 'ssh -p portnumber'