17 (3) Where the Commissioner and the registered user have agreed that an electronic communication shall be binding only on the receipt of an acknowledgement of such electronic communication, then, unless such acknowledgement has been so received within such time as agreed upon, such electronic communication shall be deemed not to have been sent. (4) As between a computer system established in terms of section 80D and any other computer system of a registered user, the lodgement of an electronic communication occurs when it enters a computer system outside the control of the originator. (5) The time of receipt of an electronic communication shall be the time when the electronic communication enters the computer— (a) where the electronic communication is by a registered user, at any office of the Zimbabwe Revenue Authority, or of the Commissioner, to whichever it was addressed, and such office shall be the place of receipt; or (b) if the electronic communication is sent by the Zimbabwe Revenue Authority or the Commissioner to a registered user, at the place of receipt that is stipulated in the user agreement. (6) Whenever any registered user is authorised to submit and sign electronically any return, record, assessment, declaration, form, notice, statement or the like, which is required to be submitted and signed in terms of this Act, such signature electronically affixed to such electronic communication and communicated to the Zimbabwe Revenue Authority or the Commissioner, shall, for the purposes of this Act, have effect as if it was affixed thereto in manuscript, and acceptance thereof shall not be denied if it is in conformity with the user agreement concluded between the Commissioner and the registered user. (7) The Commissioner may, notwithstanding anything to the contrary contained in this section, permit any registered user to submit electronically any return, record, assessment, declaration, form, notice, statement or the like, which is required to be submitted in terms of this Act, by using the Internet, and subject to such exceptions, adaptations or additional requirements as the Commissioner may stipulate or prescribe, this section shall apply to the submission of the foregoing documents using the Internet. 80J Obligations, indemnities and presumptions with respect to digital signatures (1) If the security of a digital signature allocated to a registered user has been compromised in any manner the registered user shall inform the Commissioner in writing of that fact without delay. (2) No liability shall attach to the Commissioner, the Zimbabwe Revenue Authority or any officer or employee thereof for any failure on the part of a registered user to ensure the security of the digital signature allocated to him or her and, in particular, where electronic data authenticated by a digital signature is received by the Commissioner or the Zimbabwe Revenue Authority— (a) without the authority of the registered user to whom such signature was allocated; and