SIP 433 Anonymity Disallowed
What SIP 433 means
The recipient refuses calls that withhold their number. If your outbound calls are being rejected with this, the caller ID is being suppressed somewhere between your handset and the carrier.
What SIP 433 Anonymity Disallowed actually means
The request was rejected because it was anonymous and the recipient does not accept anonymous calls. It is the protocol expression of anonymous call rejection, so the refusal is about the absence of a caller ID rather than about the caller.
What causes SIP 433 on a business phone system
- Caller ID is being withheld on the outbound callEither configured deliberately on the extension, or set as a default nobody remembers enabling.
- The presented number is stripped upstreamWhere the CLI is not one you are entitled to present, a carrier may remove it rather than refuse the call, and the call then arrives anonymous.
- A privacy header is set by the PBXA privacy setting applied at trunk level withholds the number on every call, so it affects the whole business rather than one user.
How to fix SIP 433
- Check the outbound caller ID on the extension and the trunkConfirm a valid number is being presented at both levels, since a trunk-level privacy setting overrides the extension.
- Make sure the presented number is one you ownA CLI you are not entitled to present can be stripped upstream, which makes the call anonymous without anyone choosing to withhold it.
- Remove any withhold setting applied as a defaultWithholding by default costs you answered calls, since a growing number of recipients reject anonymous callers outright.
Fixing the underlying problem
This page explains the code. These guides walk through the fix in detail.
Questions about SIP 433
What does SIP 433 Anonymity Disallowed mean?
The person you called does not accept calls from withheld numbers, and yours arrived without a caller ID. Either the number is being withheld in your configuration, or it is being stripped upstream because it is not a number you are entitled to present.
Related SIP response codes
Source. SIP 433 Anonymity Disallowed is defined in RFC 5079 and registered in the IANA SIP Parameters — Response Codes. The causes and fixes above are drawn from our own experience supporting UK business phone systems.