I do not think a warning is the right way because it prevents automatic creation of document. But here as the data is not controlled by Tryton, we can not guess that the reference will be unique per party.
|2019-04-01 18:41:39||ced||set||messageid: <firstname.lastname@example.org>|
|2019-04-01 18:41:39||ced||set||recipients: + pokoli, reviewbot|
|2019-04-01 18:41:39||ced||link||issue8244 messages|
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