Do you monitor the mirror transfer? If so, there really is no need to and if not, you can change the command and it's arguments as follows:
rsync -aqzh --delete eu-msync.centos.org::CentOS /bak/centos/CentOS
However, the command you posted does appear to be valid, so it looks like the IP address is not authorised to sync direct from the msync pool.
Anssi: Over to you.
Regards, Christopher Hawker Phone: +61 434 512 834
From: CentOS-mirror [mailto:centos-mirror-bounces@centos.org] On Behalf Of Cochrane, Bryan T Sent: Friday, 22 June 2018 9:46 PM To: centos-mirror@centos.org Subject: Re: [CentOS-mirror] Rsync giving unknown module error
rsync -ah --stats --delete eu-msync.centos.org::CentOS /bak/centos/CentOS