A rent increase notice must be in writing and served using a legally recognised method, such as handing it to you, leaving it at the rented property, or sending it by post. Electronic delivery may be acceptable where electronic service has been agreed and the legal requirements are met, but an informal text or WhatsApp message may not be enough on its own. The landlord must also send the required information to the RTB on the same day and allow the correct notice period. Keep the envelope, message and delivery evidence, and check the current RTB guidance if there is a dispute.