Hi Wissam,
Hope all is well!
You are running into this CUE default, that allows transfers to Internal (associated to CUE Mailbox) users only. Have a look, this problem can be rectified;
Internal and External Destinations
Up to Cisco Unity Express 2.0, the system AA allowed for the transfer calls to any destination,it treated the destination merely as a string of digits, and any call dialable on the associated call agent would succeed. To limit the destinations to which the AA can transfer calls (such as no calls to the PSTN), the call agent's features,such as Class of Restriction (COR) on Cisco CME were required.
**As of Cisco Unity Express Release 2.1, the system AA has a parameter to control whether calls are allowed to transfer only to internal numbers (default operation), or to internal and external numbers. Your own custom AA scripts can employ similar mechanisms to limit the valid destinations of calls. The system AA script parameter is (the value of the allowExternalTransfers parameter).
An internal number is considered to be an extension that exists in Cisco Unity Express's LDAP directory. Information that appears in LDAP includes all extensions defined and associated with a user (Configure > Users) on Cisco Unity Express. This does not include remote user (Configure > Remote Users) definitions entered on Cisco Unity Express for networking spoken name confirmation (these are not stored in LDAP). The validity of a destination number is independent of extension length or dialing plans and is not coordinated with your call agent's dial plan on what might be local extensions versus remote extensions.
Cisco Unity Express considers an extension that appears in an LDAP entry an internal destination. External destinations include everything else, such as the following:
All other extensions that exist at the local site, but do not appear in the Cisco Unity Express configuration, such as local phones/extensions that do not have mailboxes.
All VoIP destinations, such as extensions present at other sites, but a PSTN call is not required to reach them.
All PSTN destinations.
If you want to refine the destinations that the Cisco Unity Express AA can transfer calls to, you have to limit calls either on the call agent (with features such as COR), or write a custom Cisco Unity Express AA script that does the checking based on your requirements (such as perhaps extension length, or numbers starting with certain sequences such as 9).
From this good AA Design doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps5520/products_implementation_design_guide_chapter09186a00804993c2.html#wp1011696
Hope this helps!
Rob
