Just to add the next section from the RFC as well: ``` This is to maintain backwards compatibility with [RFC 2543], which did not mandate From tags. ``` Kamailio is not compatible with SIP 1.0, RFC 2543.
The addition of a From tag is mandatory according to RFC 3261, [8.1.1.3](https://www.rfc-editor.org/rfc/rfc3261#section-8.1.1.3): ``` The From field MUST contain a new "tag" parameter, chosen by the UAC. ``` I think the standard is pretty clear that its mandatory in the scope of RFC 3261.