 2019  Contract number: [ complete ]  E-mail is deemed to have been received by the receiving party on the day of dispatch of that e- mail, provided that it is sent to the e-mail address indicated in Article I.8. The sending party  must be able to prove the date of dispatch. In the event that the sending party receives a non- delivery report, it must make every effort to ensure that the other party actually receives the  communication by email or mail. In such a case, the sending party is not held in breach of its  obligation to send such communication within a specified deadline.  Mail sent to the contracting authority is deemed to have been received by the contracting  authority on the date on which the department responsible referred to in Article I.8 registers it. Formal notifications  are considered to have been received by the receiving party on the date of  receipt indicated in the proof received by the sending party that the message was delivered to  the specified recipient. 1. If provided for in the special conditions, the exchange of electronic documents (e- documents) such as requests for services, specific contracts and invoices between the  parties is automated through the use of the  e-PRIOR  platform. This platform provides  two possibilities for such exchanges: either through web services (machine-to-machine  connection) or through a web application (the  supplier portal ). 2. The contracting authority takes the necessary measures to implement and maintain  electronic systems that enable the  supplier portal  to be used effectively. 3. In the case of machine-to-machine connection, a direct connection is established  between the parties’  back offices . In this case, the parties take the measures necessary  on their side to implement and maintain electronic systems that enable the machine-to- machine connection to be used effectively. The electronic systems are specified in the  interface control document . The contractor (or leader in the case of a joint tender) must  take the necessary technical measures to set up a machine-to-machine connection and  at its own cost.  4. If communication via the  supplier portal  or via the web services (machine-to-machine  connection) is hindered by factors beyond the control of one party, it must  notify  the  other immediately and the parties must take the necessary measures to restore this  communication. 5. If it is impossible to restore the communication within two working days, one party  must  notify  the other that alternative means of communication specified in Article II.5.1  will be used until the  supplier portal  or the machine-to-machine connection is restored. 6. When a change in the  interface control document  requires adaptations, the contractor  (or leader in the case of a joint tender) has up to six months from receipt of the  notification to implement this change. This period can be shortened by mutual  agreement of the parties. This period does not apply to urgent measures required by the  security policy of the contracting authority to ensure integrity, confidentiality and non- repudiation of information and the availability of  e-PRIOR , which must be applied  immediately. 1. The parties agree that any e-document, including related attachments exchanged via  e- PRIOR :  20  II.5.4 Validity and date of e-documents  II.5.3 Submission of e-documents via e-PRIOR 