When should I sign up?

If you are moving out of the US, we recommend you sign at most two weeks prior to departure. This is because if you need to forward your incoming mail from an existing US address to your address with us (via USPS's Change of Address service), it takes them up to two weeks to get this process going.

Additionally, you may be required to go into a local USPS office to verify your identity and show your physical photo ID.

This is a USPS article that explains their Change of Address process: Change of Address

What if I haven't got a new address abroad?

You actually don’t need that address until you are ready to ship mail or packages to that address. Your address abroad would be a forwarding address and you can always add that when you place a shipment request to have your items shipped.