Single node* are you running PMG in a cluster or as a single node?
It seems I have misunderstood how it works.this is not quite right - pmgspamreport.service is used for sending out quarantine reports to the users (and cleaning up the quarantine) - pmgreport.service is used to send out the daily admin reports - both of them are invoked (unless you turn it off manually) by their respective systemd-timers.
A haven't touched any timers or services. Here is my setup:


are you running the latest version? (pmgversion -v)
Code:
# pmgversion -v
proxmox-mailgateway: 6.2-1 (API: 6.2-5/05a7829e, running kernel: 5.4.44-1-pve)
pmg-api: 6.2-5
pmg-gui: 2.2-2
pve-kernel-5.4: 6.2-4
pve-kernel-helper: 6.2-4
pve-kernel-5.3: 6.1-6
pve-kernel-5.4.44-2-pve: 5.4.44-2
pve-kernel-5.4.44-1-pve: 5.4.44-1
pve-kernel-5.4.41-1-pve: 5.4.41-1
pve-kernel-5.4.30-1-pve: 5.4.30-1
pve-kernel-5.3.18-3-pve: 5.3.18-3
pve-kernel-5.3.18-1-pve: 5.3.18-1
pve-kernel-5.3.13-2-pve: 5.3.13-2
pve-kernel-5.3.13-1-pve: 5.3.13-1
pve-kernel-5.3.10-1-pve: 5.3.10-1
clamav-daemon: 0.102.3+dfsg-0+deb10u1
libarchive-perl: 3.3.3-1
libjs-extjs: 6.0.1-10
libjs-framework7: 4.4.7-1
libpve-apiclient-perl: 3.0-3
libpve-common-perl: 6.1-3
libpve-http-server-perl: 3.0-5
libxdgmime-perl: 0.01-5
lvm2: 2.03.02-3
pmg-docs: 6.2-2
pmg-log-tracker: 2.1.6-1
postgresql-11: 11.7-0+deb10u1
proxmox-mini-journalreader: 1.1-1
proxmox-spamassassin: 3.4.4-2
proxmox-widget-toolkit: 2.2-7
pve-firmware: 3.1-1
pve-xtermjs: 4.3.0-1
zfsutils-linux: 0.8.4-pve1