diff --git a/pjsip/include/pjsip/sip_endpoint.h b/pjsip/include/pjsip/sip_endpoint.h
index 4667c1a271..c370efcac0 100644
--- a/pjsip/include/pjsip/sip_endpoint.h
+++ b/pjsip/include/pjsip/sip_endpoint.h
@@ -1,5 +1,5 @@
 /* 
- * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2008-2026 Teluu Inc. (http://www.teluu.com)
  * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -423,6 +423,18 @@ PJ_DECL(pj_status_t) pjsip_endpt_set_ext_resolver(pjsip_endpoint *endpt,
  */
 PJ_DECL(pj_dns_resolver*) pjsip_endpt_get_resolver(pjsip_endpoint *endpt);
 
+/**
+ * Get the external resolver implementation set with
+ * #pjsip_endpt_set_ext_resolver().
+ *
+ * @param endpt         The SIP endpoint instance.
+ *
+ * @return              The external resolver implementation, or NULL when
+ *                      none is set.
+ */
+PJ_DECL(pjsip_ext_resolver*) pjsip_endpt_get_ext_resolver(
+                                                pjsip_endpoint *endpt);
+
 /**
  * Mark a server address as failed for the specified duration, or clear the
  * mark. Please see #pjsip_resolver_set_server_failed() for more info.
diff --git a/pjsip/include/pjsip/sip_resolve.h b/pjsip/include/pjsip/sip_resolve.h
index 675b1a2ed0..060383e4e1 100644
--- a/pjsip/include/pjsip/sip_resolve.h
+++ b/pjsip/include/pjsip/sip_resolve.h
@@ -1,5 +1,5 @@
 /* 
- * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2008-2026 Teluu Inc. (http://www.teluu.com)
  * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -313,6 +313,20 @@ PJ_DECL(pj_status_t) pjsip_resolver_set_ext_resolver(
  */
 PJ_DECL(pj_dns_resolver*) pjsip_resolver_get_resolver(pjsip_resolver_t *res);
 
+/**
+ * Get the external resolver implementation of the SIP resolver engine.
+ *
+ * Note that application normally will use #pjsip_endpt_get_ext_resolver()
+ * instead since it does not normally have access to the SIP resolver
+ * instance.
+ *
+ * @param res       The SIP resolver engine.
+ *
+ * @return          The external resolver implementation (may be NULL)
+ */
+PJ_DECL(pjsip_ext_resolver*) pjsip_resolver_get_ext_resolver(
+                                                pjsip_resolver_t *res);
+
 /**
  * Mark a server address as failed for the specified duration, or clear the
  * mark. The mark applies to the IP address and port, whatever the transport
diff --git a/pjsip/include/pjsua-lib/pjsua.h b/pjsip/include/pjsua-lib/pjsua.h
index 3525cf1529..db34689a02 100644
--- a/pjsip/include/pjsua-lib/pjsua.h
+++ b/pjsip/include/pjsua-lib/pjsua.h
@@ -1,5 +1,5 @@
 /* 
- * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2008-2026 Teluu Inc. (http://www.teluu.com)
  * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -4783,8 +4783,12 @@ typedef struct pjsua_acc_config
     /**
      * Specify if source TCP port should be used as the initial Contact
      * address if TCP/TLS transport is used. Note that this feature will
-     * be automatically turned off when nameserver is configured because
-     * it may yield different destination address due to DNS SRV resolution.
+     * be automatically turned off when nameservers are configured
+     * (\a pjsua_config.nameserver) or when the application sets a DNS
+     * resolver or an external resolver on the SIP endpoint
+     * (#pjsip_endpt_set_resolver(),
+     * #pjsip_endpt_set_ext_resolver()), because they may yield a different
+     * destination address due to DNS SRV resolution.
      * Also some platforms are unable to report the local address of the
      * TCP socket when it is still connecting. In these cases, this
      * feature will also be turned off.
diff --git a/pjsip/include/pjsua2/account.hpp b/pjsip/include/pjsua2/account.hpp
index acf974679b..affe65ee47 100644
--- a/pjsip/include/pjsua2/account.hpp
+++ b/pjsip/include/pjsua2/account.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2013 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2013-2026 Teluu Inc. (http://www.teluu.com)
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -778,8 +778,10 @@ struct AccountNatConfig : public PersistentObject
     /**
      * Specify if source TCP port should be used as the initial Contact
      * address if TCP/TLS transport is used. Note that this feature will
-     * be automatically turned off when nameserver is configured because
-     * it may yield different destination address due to DNS SRV resolution.
+     * be automatically turned off when nameservers are configured
+     * (UaConfig::nameserver) or when the application sets a DNS resolver
+     * or an external resolver on the SIP endpoint, because they may yield
+     * a different destination address due to DNS SRV resolution.
      * Also some platforms are unable to report the local address of the
      * TCP socket when it is still connecting. In these cases, this
      * feature will also be turned off.
diff --git a/pjsip/src/pjsip/sip_endpoint.c b/pjsip/src/pjsip/sip_endpoint.c
index 6185862e28..05618f42a5 100644
--- a/pjsip/src/pjsip/sip_endpoint.c
+++ b/pjsip/src/pjsip/sip_endpoint.c
@@ -1,5 +1,5 @@
 /* 
- * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2008-2026 Teluu Inc. (http://www.teluu.com)
  * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -1347,6 +1347,16 @@ PJ_DEF(pj_dns_resolver*) pjsip_endpt_get_resolver(pjsip_endpoint *endpt)
     return pjsip_resolver_get_resolver(endpt->resolver);
 }
 
+/*
+ * Get the external resolver implementation.
+ */
+PJ_DEF(pjsip_ext_resolver*) pjsip_endpt_get_ext_resolver(
+                                                pjsip_endpoint *endpt)
+{
+    PJ_ASSERT_RETURN(endpt, NULL);
+    return pjsip_resolver_get_ext_resolver(endpt->resolver);
+}
+
 /*
  * Resolve
  */
diff --git a/pjsip/src/pjsip/sip_resolve.c b/pjsip/src/pjsip/sip_resolve.c
index cb4894a7c7..6f92752f79 100644
--- a/pjsip/src/pjsip/sip_resolve.c
+++ b/pjsip/src/pjsip/sip_resolve.c
@@ -1,5 +1,5 @@
 /* 
- * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2008-2026 Teluu Inc. (http://www.teluu.com)
  * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -190,6 +190,16 @@ PJ_DEF(pj_dns_resolver*) pjsip_resolver_get_resolver(pjsip_resolver_t *res)
 }
 
 
+/*
+ * Public API to get the external resolver implementation.
+ */
+PJ_DEF(pjsip_ext_resolver*) pjsip_resolver_get_ext_resolver(
+                                                pjsip_resolver_t *res)
+{
+    return res->ext_res;
+}
+
+
 /* Find a failed server entry. Must be called with the group lock held. */
 static int find_failed(pjsip_resolver_t *resolver, const pj_sockaddr_t *addr)
 {
diff --git a/pjsip/src/pjsua-lib/pjsua_acc.c b/pjsip/src/pjsua-lib/pjsua_acc.c
index 6d6e8f4552..d986cf1cf2 100644
--- a/pjsip/src/pjsua-lib/pjsua_acc.c
+++ b/pjsip/src/pjsua-lib/pjsua_acc.c
@@ -1,5 +1,5 @@
 /* 
- * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
+ * Copyright (C) 2008-2026 Teluu Inc. (http://www.teluu.com)
  * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
  *
  * This program is free software; you can redistribute it and/or modify
@@ -4522,16 +4522,19 @@ static pj_status_t get_uac_addr_for_sip_uri(pjsua_acc_id acc_id,
         }
 
         ip_addr_ver = get_ip_addr_ver(&dinfo.addr.host);
-        if (ip_addr_ver == 0 && pjsua_var.ua_cfg.nameserver_count) {
-            /* If nameserver is configured, PJSIP will resolve destinations
-             * by their DNS SRV record first. On the other hand, we will
-             * resolve destination with DNS A record via pj_getaddrinfo().
-             * They may yield different IP addresses, hence causing different
-             * TCP/TLS connection to be created and hence different source
+        if (ip_addr_ver == 0 &&
+            (pjsip_endpt_get_resolver(pjsua_var.endpt) ||
+             pjsip_endpt_get_ext_resolver(pjsua_var.endpt)))
+        {
+            /* With a DNS resolver or an external resolver, PJSIP may
+             * resolve destinations by their DNS SRV record first. On the other
+             * hand, we would resolve the destination with its DNS A record
+             * via pj_getaddrinfo(). They may yield different addresses,
+             * hence a different TCP/TLS connection and a different source
              * address.
              */
             PJ_LOG(4,(THIS_FILE, "Warning: cannot use source TCP/TLS socket"
-                      " address for Contact when nameserver is configured."));
+                      " address for Contact when a resolver is set."));
             goto on_return;
         }
 
diff --git a/pjsip/src/test/srv_failover_test.c b/pjsip/src/test/srv_failover_test.c
index 1216b74902..6c2230c267 100644
--- a/pjsip/src/test/srv_failover_test.c
+++ b/pjsip/src/test/srv_failover_test.c
@@ -2085,6 +2085,103 @@ static int pjsua_restore_once_case(pj_bool_t init_fails)
     return rc;
 }
 
+#if PJ_HAS_TCP
+/* An external resolver that fails every query */
+static void no_resolve(pjsip_resolver_t *resolver, pj_pool_t *pool,
+                       const pjsip_host_info *target, void *token,
+                       pjsip_resolver_callback *cb)
+{
+    PJ_UNUSED_ARG(resolver); PJ_UNUSED_ARG(pool); PJ_UNUSED_ARG(target);
+    (*cb)(PJ_ERESOLVE, token, NULL);
+}
+
+/* With an external resolver the destination may come from a DNS SRV
+ * record: the Contact takes the TCP listener's port, without a probing
+ * connection to the A record of the name.
+ */
+static int pjsua_contact_probe_case(void)
+{
+    static pjsip_ext_resolver ext = { &no_resolve };
+    pjsua_config ua_cfg;
+    pjsua_logging_config log_cfg;
+    pjsua_transport_config tcfg;
+    pjsua_transport_info tinfo;
+    pjsua_transport_id tp_id;
+    pjsua_acc_config acc_cfg;
+    pjsua_acc_id acc_id;
+    pjsip_tpmgr *tpmgr;
+    pj_pool_t *pool;
+    pj_str_t contact, uri = pj_str("sip:localhost;transport=tcp");
+    unsigned tp_cnt;
+    char *p;
+    int rc = 0;
+
+    PJ_LOG(3,(THIS_FILE, "  Contact with an external resolver"));
+
+    if (pjsua_create() != PJ_SUCCESS)
+        return -3180;
+    pjsua_config_default(&ua_cfg);
+    ua_cfg.thread_cnt = 0;
+    pjsua_logging_config_default(&log_cfg);
+    log_cfg.level = 3;
+    log_cfg.console_level = 3;
+    if (pjsua_init(&ua_cfg, &log_cfg, NULL) != PJ_SUCCESS) {
+        pjsua_destroy();
+        return -3181;
+    }
+    if (pjsip_endpt_set_ext_resolver(pjsua_get_pjsip_endpt(), &ext) !=
+        PJ_SUCCESS)
+    {
+        pjsua_destroy();
+        return -3182;
+    }
+    pjsua_transport_config_default(&tcfg);
+    tcfg.port = 0;
+    if (pjsua_transport_create(PJSIP_TRANSPORT_TCP, &tcfg,
+                               &tp_id) != PJ_SUCCESS ||
+        pjsua_start() != PJ_SUCCESS ||
+        pjsua_transport_get_info(tp_id, &tinfo) != PJ_SUCCESS)
+    {
+        pjsua_destroy();
+        return -3183;
+    }
+    pjsua_acc_config_default(&acc_cfg);
+    acc_cfg.id = pj_str("sip:test@localhost");
+    if (pjsua_acc_add(&acc_cfg, PJ_FALSE, &acc_id) != PJ_SUCCESS) {
+        pjsua_destroy();
+        return -3184;
+    }
+
+    tpmgr = pjsip_endpt_get_tpmgr(pjsua_get_pjsip_endpt());
+    tp_cnt = pjsip_tpmgr_get_transport_count(tpmgr);
+    pool = pjsua_pool_create("probe", 512, 512);
+    if (pjsua_acc_create_uac_contact(pool, &contact, acc_id,
+                                     &uri) != PJ_SUCCESS)
+    {
+        rc = -3185;
+    } else {
+        pj_str_t port;
+
+        p = pj_strchr(&contact, '@');
+        p = p ? pj_memchr(p, ':', contact.ptr + contact.slen - p) : NULL;
+        port.ptr = p ? p + 1 : NULL;
+        port.slen = p ? contact.ptr + contact.slen - port.ptr : 0;
+        if (!p || pj_strtoul(&port) != (unsigned)tinfo.local_name.port) {
+            PJ_LOG(1,(THIS_FILE, "    Contact %.*s, listener port %d",
+                      (int)contact.slen, contact.ptr, tinfo.local_name.port));
+            rc = -3186;
+        } else if (pjsip_tpmgr_get_transport_count(tpmgr) != tp_cnt) {
+            rc = -3187;
+        }
+    }
+    pj_pool_release(pool);
+    pjsua_destroy();
+    if (rc)
+        PJ_LOG(1,(THIS_FILE, "    error: Contact case failed [%d]", rc));
+    return rc;
+}
+#endif
+
 int srv_failover_pjsua_test(void)
 {
     int rc;
@@ -2106,6 +2203,10 @@ int srv_failover_pjsua_test(void)
         rc = pjsua_restore_once_case(PJ_FALSE);
     if (rc == 0)
         rc = pjsua_restore_once_case(PJ_TRUE);
+#if PJ_HAS_TCP
+    if (rc == 0)
+        rc = pjsua_contact_probe_case();
+#endif
 
     restore_test_endpt();
     return rc;