We have an enquiry from Giles du Boulay, Chairman of the German Colonies P.S.
"I am enquiring as to whether anyone in the France & Colonies PS might be able to help with information about the ‘Post Plombage’ handstamp on the letter, scans attached. The sealed letter, possibly a letter accompanying a parcel, was sent from Danzig to Königsberg in 1811, during the period when Danzig was occupied by Napoleonic troops.
My internet search immediately returned this AI generated explanation
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Old French postmarks with "Plombage" indicated the sealing of mail with lead. These postmarks would have been used to signify the mail was secured and not to be opened before reaching its destination. Plombage was a method of sealing letters and packages using lead, which was commonly used in France during the 18th and 19th centuries
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Whether that is true or not I do not know."
Is anyone able to help?
roger