Update networking layer w/ CURL and emscripten impl

External/curl-8.17.0/docs/libcurl/opts/CURLOPT_MAIL_RCPT.md

@@ -0,0 +1,91 @@
+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_MAIL_RCPT
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_MAIL_AUTH (3)
+  - CURLOPT_MAIL_FROM (3)
+Protocol:
+  - SMTP
+Added-in: 7.20.0
+---
+
+# NAME
+
+CURLOPT_MAIL_RCPT - list of SMTP mail recipients
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MAIL_RCPT,
+                          struct curl_slist *rcpts);
+~~~
+
+# DESCRIPTION
+
+Pass a pointer to a linked list of recipients to pass to the server in your
+SMTP mail request. The linked list should be a fully valid list of
+**struct curl_slist** structs properly filled in. Use curl_slist_append(3) to
+create the list and curl_slist_free_all(3) to clean up an entire list.
+
+libcurl does not copy the list, it needs to be kept around until after the
+transfer has completed.
+
+When performing a mail transfer, each recipient should be specified within a
+pair of angled brackets (\<\>), however, should you not use an angled bracket
+as the first character libcurl assumes you provided a single email address and
+encloses that address within brackets for you.
+
+In order to specify DSN parameters (as per RFC 3461), the address has to be
+written in angled brackets, followed by the parameters.
+
+When performing an address verification (**VRFY** command), each recipient
+should be specified as the username or username plus domain (as per Section
+3.5 of RFC 5321).
+
+When performing a mailing list expand (**EXPN** command), each recipient
+should be specified using the mailing list name, such as `Friends` or
+`London-Office`.
+
+Using this option multiple times makes the last set list override the previous
+ones. Set it to NULL to disable its use again.
+
+# DEFAULT
+
+NULL
+
+# %PROTOCOLS%
+
+# EXAMPLE
+
+~~~c
+int main(void)
+{
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    CURLcode res;
+    struct curl_slist *list;
+    list = curl_slist_append(NULL, "root@localhost");
+    list = curl_slist_append(list, "person@example.com");
+    list = curl_slist_append(list, "<other@example.com> NOTIFY=SUCCESS");
+    curl_easy_setopt(curl, CURLOPT_URL, "smtp://example.com/");
+    curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, list);
+    res = curl_easy_perform(curl);
+    curl_slist_free_all(list);
+    curl_easy_cleanup(curl);
+  }
+}
+~~~
+
+# %AVAILABILITY%
+
+# RETURN VALUE
+
+curl_easy_setopt(3) returns a CURLcode indicating success or error.
+
+CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
+libcurl-errors(3).