Block outside calls from accessing Voice Mail?

[uptime1]

My customer wants the same simple password for all voicemail boxes, but I'm concerned anyone calling from the outside could easily hack in. They don't need access to voicemail when outside the office. Is there a way to block voicemail from being accessed through a SIP trunk?

 

[YiannisH_3CX]

There are two ways to access a voicemail through a SIP trunk or an external number,
The first is creating inbound rules for the voicemail accounts you want to access so since there is no need for that just remove the inbound rules for this if any.
The second way is by direct dialing through a digital receptionist. When an external call comes in and is connected to a digital receptionist the caller has the option to dial an extension directly while the prompt message is heard. From there the external caller can dial 999 ( or whatever the vmail number is) and connect to the voice mail system where he will be asked for the extension number and identification number for the specific extension.

direct dialing can be disabled by going to troubleshooting>Parameters, in the search box type grammar, a parameter called IVR_DIRECT_DIALING_GRAMMAR will appear and you can change the value from [0-9]{3} (default) to [0-9]{1}

Note that this will disable all direct dialing though.