There are in fact some places where you would clear customs before departure to the US. Several airports in Canada as well as some Caribbean airports (Montreal, Nassau, and Bermuda to name a few).
The procedure is the same whether you clear customs before departure or after arrival. It is still US Customs agents that process you. You and your luggage will also be screened as usual. Sometimes before customs and sometimes after.
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Customs clearance only occurs on arrival in a country, not departure, so there is no procedure for departure.
Regards,
Dan
References :
There are in fact some places where you would clear customs before departure to the US. Several airports in Canada as well as some Caribbean airports (Montreal, Nassau, and Bermuda to name a few).
The procedure is the same whether you clear customs before departure or after arrival. It is still US Customs agents that process you. You and your luggage will also be screened as usual. Sometimes before customs and sometimes after.
References :