From Porto you would have to use the Portuguese post office, or ask one the the luggage transport companies on the Portuguese route, like Tuitrans and Top Santiago if they would do this.
Also check out Luggage Driver.
But what supplies would...
Hi! I'll be walking the Camino Portugues from Porto with my family. Do you know if it's possible for me to mail our suitcase to Redondela/Tui for ahead of us? Then once we get there and swap out supplies, mail it again to Santiago?
Basically...
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