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If they use transaction/wallet listener, how do they detect deposit transactions when their services are not running, do they fetch blocks at every height to scan for deposits to avoid any missing? Thanks,

If they use transaction/wallet listener, how do they detect deposit transactions when their services are not running, do they fetch blocks at every height to avoid any missing? Thanks,

If they use transaction/wallet listener, how do they detect deposit transactions when their services are not running, do they fetch blocks at every height to scan for deposits to avoid any missing? Thanks,

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How do exchange sites know all user deposit transactions?

If they use transaction/wallet listener, how do they detect deposit transactions when their services are not running, do they fetch blocks at every height to avoid any missing? Thanks,