VPS providers generally (don't know about GCP) lift port restrictions if you write them and request it explicitly. At least Vultr and Linode will also communic

VPS providers generally (don't know about GCP) lift port restrictions if you write them and request it explicitly. At least Vultr and Linode will also communicate with other big providers (e.g. Gmail or Outlook.com) in case you have delivery issues due to history of the IP addressor subnet before you took it over.