How to Check for and Block “Anonymous” Callers
If you want to block calls from “anonymous” callers, you can leverage the “CallerID Blacklist” feature. From the 3CX Management Console:
- Go to “Settings” → “Blacklisted Numbers”.
- Click on the “Add” button.
- In the “Blacklist” window:
- Set the “Incoming caller ID to be blocked” field to the value “Anonymous” or “anonymous”. In this case, we will set the field to “*nonymous” to match both values (The * will act as a wildcard).
- Set the “Description” field for informational purposes.
At this stage, you can check an inbound call and you should see that the anonymous call is rejected correctly.
This is a typical INVITE from a caller whose CallerID is hidden:
v: SIP/2.0/UDP 188.8.131.52:5080;branch=z9hG4bK-8b2f242058b3802ce60c00f1db2b8201
f: "Anonymous" <sip:firstname.lastname@example.org>;tag=3727603634-668969
CSeq: 1 INVITE
Sometimes your telecom provider will deliver the call with “unknown” or some other text instead of “anonymous” – simply examine the incoming INVITE particularly the “From” field. You can then add or adjust your Blacklist rule accordingly.