RFC 3323 gives the anonymous From header form "Anonymous" <sip:anonymous@anonymous.invalid> with a tag, using the reserved .invalid domain.

Checked 2026-09-25

Vendor
IETF
Product
SIP
Subsystem
privacy
Deployment
any
Region
not restricted
Release range
RFC 3323
Checked
2026-09-25

Sources

Cite this note

APA

WarmTransfer. (2026, September 25). Wrong or missing caller ID on outbound calls: source note caller-id-presentation-problems-anonymous-from-form. WarmTransfer. https://warmtransfer.net/knowledge/claims/caller-id-presentation-problems-anonymous-from-form

BibTeX

@misc{warmtransfer-claim-caller-id-presentation-problems-anonymous-from-form,
  title  = {Wrong or missing caller ID on outbound calls: source note caller-id-presentation-problems-anonymous-from-form},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/claims/caller-id-presentation-problems-anonymous-from-form},
  note   = {Source note caller-id-presentation-problems-anonymous-from-form, checked 2026-09-25}
}

Read in context