Under the EIO Directive: Besides the grounds of non-recognition/execution provided under art. 11 Directive 2014/41/EU, recognition and execution might be refused where the measure would be contrary to the fundamental principles of Luxembourg Law and where the measure would not be authorized in similar domestic cases.
Under instruments of MLA: To be requested by international letters rogatory. Contents: an indication of the authority making the request; a summary of the facts; confirmation that a lawful interception order or warrant has been issued in connection with a criminal investigation; information for the purpose of identifying the subject of the interception; an indication of the criminal conduct under investigation; the desired duration of the interception; and where applicable, the provision of sufficient technical data to ensure that the request can be met.
Duration limited to one month by law; prolongation possible on a monthly basis as long as necessary, however no longer than one year.
Relevant mailings to be copied to the file under authority of the examining magistrate. Execution of the measure in conformity with the procedure applicable in the requesting State : possible as a matter of principle; to be assessed on a case by case basis. Relevant formalities to be expressly indicated.
In any event, duration limited to one month by law; prolongation possible on a monthly basis as long as necessary, however no longer than one year.