See also chapter III.S.4. "Spheres of risk and apportioning the burden of proof". R. 126 EPC (notification by post) and R. 127 EPC (electronic notification) lay down rules on the burden of proof in case of dispute (for the amended versions of these provisions, see CA/D 6/14 in OJ 2015, A17, and the explanatory notice in OJ 2015, A36, points 3.1 ff). On the requisite standard of proof, see also in chapter III.G.4.3.7.

In T 632/95 the board pointed out that the burden of proving that a document had been received lay with the party submitting the document just as, vice versa, the EPO bore the burden of proving receipt of the documents it issued.

It has to be observed that a party submitting that something has not happened is faced with the difficulty of proving this allegation. The party can essentially presume what could have happened or what normally would have been done if a letter had been received, in order to cast doubt upon the EPO's evidence, but it is hardly ever possible to file compelling evidence that the letter was not received. The EPO is also in a difficult situation if an applicant submits that it has not received a communication. The EPO then has to start enquiries with the postal services and rely on the information obtained. Since details are not given, this information is usually unsatisfactory. After a certain period the relevant information may not even be obtainable at all. However, this ought not to be to the detriment of the applicant, specifically not where communication noting a loss of rights is concerned. These problems could be avoided if such communications were delivered by registered letter with advice of delivery (J 9/05 and J 18/05).

According to the German version of R. 126 (2) EPC (former R. 78(2) EPC 1973), the EPO must in a case of doubt ("im Zweifel") establish the date on which the letter was delivered to the addressee. In T 247/98 the board decided that, when establishing the meaning of the term "im Zweifel" in the German version, account should be taken of the French and English versions, which assumed that there was a dispute ("en cas de contestation", "in the event of any dispute"). From the general principles concerning the burden of presentation which fell on the parties, it followed that a party seeking the application of a legal provision favourable to its interests had to set out the facts justifying such application, even if it did not ultimately bear the burden of proof for those facts. Although, in the event of a dispute within the meaning of said rule, the burden of proof for the date of delivery fell on the EPO, this could not be taken to mean that a party wishing to rely on the late delivery of a letter from the EPO had no obligation to contribute to the clarification of circumstances within its own sphere of activity but could sit back, as it were, and wait to see whether the EPO succeeded in ascertaining when the letter had been delivered to the party. A dispute ("Zweifel" 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.

In J 3/14 the board stated that, in a situation where the representative submitted that he had not received a communication, the EPO bore the burden of proof. In the board's opinion, it had at least been made plausible that the postal authorities erroneously delivered the letter to an unauthorised person in view of an authorisation which seemed to allow the collection of "all registered mail". The appellant also brought evidence as to the absence of its representative from her place of business. The board concluded that, in cases where the EPO bore the burden of proof, the applicant had to be given the benefit of the doubt. If doubts remained about what had really happened, this could not be to the detriment of the applicant. This applied all the more in a situation like the one at issue where the refusal of the application was the immediate consequence for the applicant.

In T 50/12 the board held that, by producing the advice of delivery, the EPO had fulfilled its duty under R. 126(2) EPC to assess the actual date of delivery to the addressee. Hence, the burden of proof lay with the appellant. To prove the later delivery, the appellant submitted two documents, neither of which convinced the board of appeal.

Under the EPC, the date of receipt of an item at the EPO is critical when assessing compliance with a time limit. The burden of proof that a filing has been effected falls on the filing party. The impossibility of furnishing proof of a higher probability that an item was filed than that it was not filed, must therefore count against the filing party – as found by the board in T 1200/01. In this particular case, the available evidence did not convince the board that there was a higher degree of probability that the alleged filing had taken place than that it had not. Contrary to the decision in T 1200/01, the board in T 2454/11 found that the strict allocation of the burden of proof to the sender of correspondence addressed to the EPO could not be mitigated by weighing up the probability of receipt. Such an approach to examining the issue would seriously jeopardise legal certainty and water down the standard of legal clarity required in formal procedures such as those before the EPO. The need in disputed cases to interpret the vague legal notion of probability and the judicial exercise of ascertaining whether a greater or lesser likelihood was to be presumed would result in a wide variety of possibly contradictory approaches to the issue. Such inconsistencies would run counter to the need for a transparent and straightforward procedure and therefore had to be avoided in the interests of the public and third parties involved in the proceedings. Consequently, a high probability of delivery could not be a factor in deciding whether correspondence had actually been received. Rather, it was for the sender to prove such receipt to the board's satisfaction.

In J 10/91 the board held that if a letter and attached cheque in payment of a fee, had been lost without further evidence or any high probability that it had been lost in the EPO, the risk was then borne by the sender. Even conclusive evidence that something had been posted could not be treated as sufficient to prove that a document had been received by the EPO. In this respect, the board in J 8/93 stated that if the post failed to deliver a document, the applicant would suffer the consequences for failing to file that document.

Under R. 125(4) EPC (former R. 82 EPC 1973; paragraph 4 not amended by CA/D 6/14) the burden of proof that documents have been duly notified to the parties lies with the EPO. In T 580/06 the question was raised whether the "OK" reference on the transmission sheet of a faxed document was sufficient proof of receipt. In the absence of relevant EPO case law, the board drew on procedural principles developed for notification by fax in German law, the fax transmission in question having arisen in the territory of the Federal Republic of Germany. In line with the German case law on that issue, the board recognised that an up-to-date objective assessment of the question of receipt of a fax by the addressee needed to take into account the technology underlying faxes. The high reliability of this technology nowadays was based amongst other things on established technical protocols, according to which modern fax machines operated. On the basis of various considerations the board reached the conclusion that the "OK" reference on the transmission sheet of a fax was to be regarded as proof of an error-free and complete transmission, through which the fax had entered into the area of responsibility of the representative. Once the fax had entered the area of responsibility of the addressee indicated by the reference "OK", then a transfer of risk took place so that the recipient bore the risks in his own sphere.

Under R. 125(4) and 126(2) EPC the EPO has to bear not only the risks arising within its own sphere but also the "transport" risks, e.g. of post going astray on its way to the addressee. But here a distinction must be drawn between risks borne by the EPO and those for which the addressee has organisational responsibility and power (T 1535/10, see headnote). See chapter III.S.4. "Spheres of risk and apportioning the burden of proof". This same division of risk applies also to newer, electronic means of notification under R. 127 EPC (see also the EPO's explanatory notice in OJ 2015, A36, especially as regards amendment of R. 124 EPC to R. 127 EPC and R. 129 EPC).