Depending on the PBX and the respective telephone (e.g. feature-added telephone), the incoming of ixi-UMS messages (faxes, voice mails, SMS) can be signaled at the telephone of the user. This is the so-called feature MWI (Message Waiting Indication).
For switching on the indication at the telephone, the ixi-UMS Business transmits a corresponding signal to the PBX. At last, the MWI is switched on by the PBX.
For switching off the indication at the telephone, a so-called "alert-message" is sent to the ixi-UMS Business Server by the mail client. The ixi-UMS Business Server passes the information on to the PBX. By doing so the PBX is caused to delete the MWI at the respective user's telephone.
For information about the addressing and the format of these alert-message, please have alook at the MWI Signaling. You can also get information about the requirements there.
Information on the format and setting up of this alert message can be found in the manual under "Additional Informations - MWI - Signaling"