For full list including DSM 6 see What websites does my Synology NAS connect to when running services or updating software?
Synology HDD/SSD Update Pack Download Site
- dataupdate7.synology.com
- dataautoupdate7.synology.com
- dataautoupdate7.synology.cn (Only for China)
DSM Update Download Site
- global.download.synology.com
- global.synologydownload.com
- update7.synology.com
- autoupdate7.synology.com
- autoupdate7.synology.cn (Only for China)
List of sub domains owned by Synology: https://subdomainfinder.c99.nl/scans/2023-08-18/synology.com