Rule 126 of the European Patent Convention (EPC) historically provided that where notification was made by the European Patent Office (EPO) by registered letter, the letter was deemed to have been delivered to the addressee on the tenth day following its handover to the postal service provider, unless it had failed to reach the addressee or had reached him/her at a later date. As the EPO's main time limits are triggered by a communication received by registered letter, this rule meant that a reply to a communication sent by registered letter could still be validly filed within 10 days from its actual receipt, hence the "10-day rule" name for this Rule 126 EPC.
The recent and massive deployment of electronic means of communication allowing communications to be sent electronically led the EPO to abandon this rule with effect as from November 1st, 2023. For documents notified by postal services or electronic means on or after November 1st, 2023, documents will be deemed to have been notified to the addressee on the date they bear. Safeguards are of course provided for in cases where a document is not received or is received exceptionally late (more than 7 days after the date it bears). In the event of a dispute concerning the delivery of a document, the EPO will retain the obligation to prove that the document was received and the date on which it was received.