I suggest that the mailbox of each SnomOne extension facilitate an option for the sending of fax. Example, press 2 to send a fax. Fax would then be stored in the individual mailbox. I would expect that the fax would then be treated as a message and should be able to be sent to an email address.
I suggest you create an option that allows for a secret code to be requested -based upon service flag configuration- before a transfer to any specified extension. In other words, when this option is activated and an extension is dialed, or selected from the name's directory, a code is requested before transfer.