Law 39/2015:
Article 41. General conditions for the practice of notifications .
“1. Notifications should preferably be made by electronic means and, in any case, when the interested party is obliged to receive them in this way.
However, administrations may practice notifications by non-electronic means in the following cases:
a) When the notification is made on the occasion of the spontaneous appearance of the interested party or his representative in the assistance offices in matters of registration and request the communication or personal notification at that time. [...]
Regulations may establish the obligation to carry out electronic notifications for certain procedures and for certain groups of individuals who, due to their economic, technical capacity, professional dedication or other reasons, are proven to have access and availability of the necessary electronic means. ”
Article 44. Unsuccessful notification .
"When those interested in a procedure are unknown, the place of the notification is unknown or, once it has been tried, it has not been possible to practice, the notification must be made by means of a published announcement in the "Official State Gazette". Likewise, in advance and on an optional basis, the administrations may publish an announcement in the official bulletin of the Autonomous Community or of the province, on the edict board of the City Council of the last address of the interested party or of the consulate or section. consular officer of the corresponding embassy. The public administrations may establish other complementary forms of notification through the other means of dissemination, which do not exclude the obligation to publish the announcement corresponding to the "Official State Gazette". "