Next update, NostrSync backup service will come with custom relays option, along with the capability to store backups obtained from external sources. 

This app allows you to fetch, download, manage, update, and broadcast your Nostr data across all existing relays without any external servers. More to come! 🤙
https://image.nostr.build/7d2b5e4f556852b0dd1819f712a87836042131fb34ace378617e9371e870d9d0.jpg