All parties must provide the other parties with a complete copy of the evidence they intend to rely upon at least 7 days before the hearing or 5 days in the case of responding evidence. Evidence should be emailed to the LTB at LTB.Evidence@ontario.ca and to the tenant. If email is not possible it can be mailed or courier it to the address identified in the Notice of Hearing. Files emailed to the LTB must be in one of the following formats: PDF, Word, Excel, JPG, MP3, MP4 or MOV. For more information on Evidence visit the LTB’s Practice Direction on Evidence –https://tribunalsontario.ca/documents/ltb/Practice%20Directions/Practice%20Direction%20on%20Evidence.html#filetype
This is a link to a Landlord and Tenant Board case from CanLII that makes reference to text message as a usual means of communication between the landlord and (applying) tenant, for your reference: