Under R. 126(2) EPC, in the event of any dispute, it is incumbent on the European Patent Office to establish that a letter has reached its destination or to establish the date on which it was delivered to the addressee, as the case may be. In cases where the EPO is not able to prove the actual date of notification, a letter, for instance, sent by the addressee himself which indicates the date of receipt is accepted as proof. If it is evident from an addressee's reply that he has received the document, although he does not mention the date of its notification, the date on which that reply was written is to be regarded as the date of notification (Guidelines E‑II, 2.6 – November 2018 version, regarding R. 125(4) EPC). The risk associated with electronic notification under R. 127 EPC is apportioned in the same way.

In T 1535/10 the board held that responsibility for obstacles to and delays in the receipt of decisions to be notified under R. 126(1) EPC had to be assigned according to spheres of risk. The Office was liable for both the risks arising in its own sphere and "transport risks". However, it distinguished such risks from those within the recipient's sphere of organisation and influence, e.g. the risk that employees or other authorised recipients failed to forward a letter delivered to the business address, or delayed in doing so. For a presumption that a letter had entered the recipient's sphere of organisation and influence, it sufficed that it had been delivered to his address and that he was in a position to take note of it, irrespective of whether he had actually taken (final) possession of it and noted its content (see also T 580/06).

In J 14/14, in keeping with the bulk of the boards' case law, the Legal Board held that it was clear from the wording of R. 126(2) EPC that, in the event of any dispute as to whether a notification has been received by the addressee, the onus was on the EPO to establish the fact and date of delivery. In the case in hand, the only proof of delivery that the EPO had in respect of the communication in question was a letter from Deutsche Post, referring to a registered letter sent to the appellant's representative and stating that it had been delivered to a person authorised to receive it. This was deemed insufficient to fulfil the requirements of R. 126(2) EPC since there was no proof that the appellant's representative or any other named individual had signed a document acknowledging receipt of the letter and no communication from the foreign postal service was disclosed (see also J 9/05 and J 18/05, where a similar confirmation letter by Deutsche Post was held not to be sufficient to prove the receipt of an EPO notification since the appellant had filed a considerable amount of counter-evidence and pointed out specific reasons why the letter might not have been received by the representative's office).

In T 529/09, however, the board held, distinguishing the case in hand from J 9/05 and J 18/05, that unlike in these cases, the appellant had not submitted any further arguments or evidence in order to demonstrate that the Deutsche Post's confirmation had failed to establish that the registered letter had reached its destination. The evidence on file therefore had to be regarded as sufficiently reliable and complete for proving the proper delivery of the letter (see also T 1304/07, T 1934/16).

In T 247/98 the board stated that when establishing the meaning of the term "im Zweifel" in the German version of R. 126(2) EPC, account should be taken of the French and English versions, which assume that there is a dispute ('en cas de contestation', 'in the event of any dispute'). A dispute ('Zweifel', literally 'doubt' in the German version) within the meaning of this rule could only arise if it was maintained that a letter had in fact been received more than ten days following its posting. The mere absence of the advice of delivery or the receipt from the file was not in itself sufficient to give rise to a dispute ('Zweifel') within the meaning of this rule. In T 2054/15 the board stated that the burden of proof on the EPO cannot be taken to mean that the party is under no obligation to help clarify the circumstances within its own sphere of responsibility.