Words are not fixed, the meaning of "mail" has changed because of what you see as missuse. If you say "mail" not everyone is entirely clear on what you mean. For those reasons we often refer to it just a "chain" today.
To be sure, if i was reffering to it in a paper I would use "mail" or perhaps even "mayle", but I'd also refer to a burh-geat, instead of a "Burgh Gate".
More on topic; If this is mail (or chain, or interlinked-rivited-closed-rings) then it would seem to be a full hauberk. In which case the thorax would seem to be leather or cloth. Not that heavy, but it doesn't solve the other problems you mentioned. One possible vector for the mail is via Celtic mercenaries, though.
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