[Users] Event: keep-alive

Hello, Certain user agents send a NOTIFY message with the header Event: keep-alive Our server responds with a 501 Not Implemented message. Does anyone know if this is correct behaviour? Should it respond with a 200 Ok in order for the user agent to work? I am assuming that any response should be enough to keep the NAT binding alive, but maybe I am wrong. thank you for any help. George Papadopoulos Disclaimer The information in this e-mail and any attachments is confidential. It is intended solely for the attention and use of the named addressee(s). If you are not the intended recipient, or person responsible for delivering this information to the intended recipient, please notify the sender immediately. Unless you are the intended recipient or his/her representative you are not authorized to, and must not, read, copy, distribute, use or retain this message or any part of it. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses.