when kamailio 5.8.6 got the follow SIP message.

INVITE sip:026774800@kamnet:5060;user=phone SIP/2.0
Via: SIP/2.0/UDP 10.25.206.73:5060;branch=z9hG4bK6204h710copg0h2s34a0.1
From: <sip:506555021@kamnet:5060;transport=UDP;user=phone>;tag=BN-1778920881-1-1752995491-343935404
To: <urn:service:sos.police@kamnet>
Call-ID: 5f6d530-13f3cbf9-fb215-7f1546651f58-4d0f660a-13c4-764
CSeq: 1 INVITE
X-SessionId: -1778920881
User-Agent: BN4000-3.9.2-706
Max-Forwards: 60
Supported: norefersub,timer,100rel,199
P-Asserted-Identity: <sip:506555021@hotmobile.co.il:5060;transport=UDP;user=phone>
P-Asserted-Identity: <tel:506555021;phone-context=+972>
Contact: <sip:10.25.206.73:5060;yop=00.00.84CE62D9.0000.7009;transport=udp>
P-Early-Media: supported
P-Access-Network-Info: 3GPP-E-UTRAN-FDD;utran-cell-id-3gpp=425074efe02c6a01
Content-Disposition: session;handling=required
Allow: INVITE,CANCEL,ACK,BYE,OPTIONS,INFO,PRACK,UPDATE,REFER,NOTIFY
Content-Type: application/sdp
Content-Length: 207

v=0
o=BN4000 0 0 IN IP4 10.9.21.56
s=-
c=IN IP4 10.9.21.56
t=0 0
m=audio 54732 RTP/AVP 8 0 101
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:101 telephone-event/8000
a=maxptime:20
a=ptime:20

the TO  To: <urn:service:sos.police@kamnet>, the problem is kamailio 5.8.6 response with 400 bad to header but kamailio 5.7.5 continue with normal call.

here you can see the sanity log for both kamailio:

kamailio 5.8.6
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:254]: check_ruri_sip_version(): check_ruri_sip_version entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:278]: check_ruri_sip_version(): check_ruri_sip_version passed
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:286]: check_ruri_scheme(): check_ruri_scheme entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:305]: check_ruri_scheme(): check_ruri_scheme passed
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:327]: check_required_headers(): check_required_headers entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:350]: check_required_headers(): check_required_headers passed
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:519]: check_cseq_method(): check_cseq_method entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:553]: check_cseq_method(): check_cseq_method passed
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:563]: check_cseq_value(): check_cseq_value entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:591]: check_cseq_value(): check_cseq_value passed
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:601]: check_cl(): check_cl entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:626]: check_cl(): check_cl passed
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:643]: check_expires_value(): check_expires_value entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:679]: check_expires_value(): no expires header found
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:776]: check_parse_uris(): check_parse_uris entered
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:780]: check_parse_uris(): parsing ruri
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:793]: check_parse_uris(): looking up From header
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: sanity [sanity.c:808]: check_parse_uris(): looking up To header
Jul 20 17:08:15 vm-tkamprov-n 671587  DEBUG: <core> [core/parser/parse_uri.c:1369]: parse_uri(): bad char '@' in state 5 parsed: <urn:service:sos.police> (22) / <urn:service:sos.police@kamnet> (29)
Jul 20 17:08:15 vm-tkamprov-n 671587  ERROR: <core> [core/parser/parse_to.c:81]: parse_to_uri(): failed to parse To uri
Jul 20 17:08:15 vm-tkamprov-n 671587  WARNING: sanity [sanity.c:810]: check_parse_uris(): invalid To header or uri






kamailio 5.7.5
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:253]: check_ruri_sip_version(): check_ruri_sip_version entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:277]: check_ruri_sip_version(): check_ruri_sip_version passed
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:285]: check_ruri_scheme(): check_ruri_scheme entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:304]: check_ruri_scheme(): check_ruri_scheme passed
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:326]: check_required_headers(): check_required_headers entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:349]: check_required_headers(): check_required_headers passed
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:518]: check_cseq_method(): check_cseq_method entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:552]: check_cseq_method(): check_cseq_method passed
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:562]: check_cseq_value(): check_cseq_value entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:590]: check_cseq_value(): check_cseq_value passed
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:600]: check_cl(): check_cl entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:625]: check_cl(): check_cl passed
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:638]: check_expires_value(): check_expires_value entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:674]: check_expires_value(): no expires header found
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:771]: check_parse_uris(): check_parse_uris entered
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:775]: check_parse_uris(): parsing ruri
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:788]: check_parse_uris(): looking up From header
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:803]: check_parse_uris(): looking up To header
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity.c:853]: check_parse_uris(): check_parse_uris passed
Jul 20 17:00:51 vm-tkamprov-n 662105  DEBUG: sanity [sanity_mod.c:252]: w_sanity_check(): sanity checks result: 1

Thanks