Thank you for the advice, @miconda. I believe this may be a bug in PJSIP's header parsing (https://trac.pjsip.org/repos/browser/pjproject/trunk/pjsip/src/pjsip/sip_par...). I'm not a C coder, but I've learned to troll through the code until I find something reasonable. Perhaps you can spot something in there. I have requested to join the PJSIP mailing list to ask about this issue.
I asked originally about the quoting because I noticed Kamailio does quote the "received" parameter in the Contact header when it's sent back to a UAC: ``` SIP/2.0 200 OK. v: SIP/2.0/UDP 10.1.1.1:5060;rport=5060;branch=z9hG4bKPjCF9fXKT.TUYCvcI8L4gj70nJMeMYZwXR;received=10.1.1.2. f: "Test" sip:test@example.com;tag=fFfFWPFbM71fqOQLp9biV6jtcZy-M3Ja. t: "Test" sip:test@example.com;tag=ac90c8713242940d16090974f12e49d3.d0ca. i: ZU0l8HgtMQ80aFG.P6LdNwCTtFiAlTBr. CSeq: 895 REGISTER. Contact: sip:test@10.1.1.1:5060;ob;expires=900;received="sip:10.1.1.2:5060". Supported: outbound. Content-Length: 0. ```
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