smtp: Allow RCPT TO command to fail for some recipients

Introduces CURLOPT_MAIL_RCPT_ALLLOWFAILS.

Verified with the new tests 3002-3007

Closes #4816

6 files changed, 94 insertions, 13 deletions

diff --git a/docs/KNOWN_BUGS b/docs/KNOWN_BUGS
index 01c19d412..ef3594672 100644
--- a/docs/KNOWN_BUGS
+++ b/docs/KNOWN_BUGS
@@ -35,9 +35,8 @@ problems may have been fixed or changed somewhat since this was written!
  3. Email protocols
  3.1 IMAP SEARCH ALL truncated response
  3.2 No disconnect command
- 3.3 SMTP to multiple recipients
- 3.4 POP3 expects "CRLF.CRLF" eob for some single-line responses
- 3.5 AUTH PLAIN for SMTP is not working on all servers
+ 3.3 POP3 expects "CRLF.CRLF" eob for some single-line responses
+ 3.4 AUTH PLAIN for SMTP is not working on all servers
 
  4. Command line
  4.1 -J and -O with %-encoded file names
@@ -276,21 +275,13 @@ problems may have been fixed or changed somewhat since this was written!
  The disconnect commands (LOGOUT and QUIT) may not be sent by IMAP, POP3 and
  SMTP if a failure occurs during the authentication phase of a connection.
 
-3.3 SMTP to multiple recipients
-
- When sending data to multiple recipients, curl will abort and return failure
- if one of the recipients indicate failure (on the "RCPT TO"
- command). Ordinary mail programs would proceed and still send to the ones
- that can receive data. This is subject for change in the future.
- https://curl.haxx.se/bug/view.cgi?id=1116
-
-3.4 POP3 expects "CRLF.CRLF" eob for some single-line responses
+3.3 POP3 expects "CRLF.CRLF" eob for some single-line responses
 
  You have to tell libcurl not to expect a body, when dealing with one line
  response commands. Please see the POP3 examples and test cases which show
  this for the NOOP and DELE commands. https://curl.haxx.se/bug/?i=740
 
-3.5 AUTH PLAIN for SMTP is not working on all servers
+3.4 AUTH PLAIN for SMTP is not working on all servers
 
  Specifying "--login-options AUTH=PLAIN" on the command line doesn't seem to
  work correctly.
diff --git a/docs/cmdline-opts/mail-rcpt-allowfails.d b/docs/cmdline-opts/mail-rcpt-allowfails.d
new file mode 100644
index 000000000..b5723df34
--- /dev/null
+++ b/docs/cmdline-opts/mail-rcpt-allowfails.d
@@ -0,0 +1,15 @@
+Long: mail-rcpt-allowfails
+Help: Allow RCPT TO command to fail for some recipients
+Protocols: SMTP
+Added: 7.69.0
+---
+When sending data to multiple recipients, by default curl will abort SMTP
+conversation if at least one of the recipients causes RCPT TO command to
+return an error.
+
+The default behavior can be changed by passing --mail-rcpt-allowfails
+command-line option which will make curl ignore errors and proceed with the
+remaining valid recipients.
+
+In case when all recipients cause RCPT TO command to fail, curl will abort SMTP
+conversation and return the error received from to the last RCPT TO command.
\ No newline at end of file
diff --git a/docs/libcurl/curl_easy_setopt.3 b/docs/libcurl/curl_easy_setopt.3
index ca558e864..099ca658c 100644
--- a/docs/libcurl/curl_easy_setopt.3
+++ b/docs/libcurl/curl_easy_setopt.3
@@ -357,6 +357,8 @@ Address of the sender. See \fICURLOPT_MAIL_FROM(3)\fP
 Address of the recipients. See \fICURLOPT_MAIL_RCPT(3)\fP
 .IP CURLOPT_MAIL_AUTH
 Authentication address. See \fICURLOPT_MAIL_AUTH(3)\fP
+.IP CURLOPT_MAIL_RCPT_ALLLOWFAILS
+Allow RCPT TO command to fail for some recipients. See \fICURLOPT_MAIL_RCPT_ALLLOWFAILS(3)\fP
 .SH TFTP OPTIONS
 .IP CURLOPT_TFTP_BLKSIZE
 TFTP block size. See \fICURLOPT_TFTP_BLKSIZE(3)\fP
diff --git a/docs/libcurl/opts/CURLOPT_MAIL_RCPT_ALLLOWFAILS.3 b/docs/libcurl/opts/CURLOPT_MAIL_RCPT_ALLLOWFAILS.3
new file mode 100644
index 000000000..aeff2955a
--- /dev/null
+++ b/docs/libcurl/opts/CURLOPT_MAIL_RCPT_ALLLOWFAILS.3
@@ -0,0 +1,71 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at https://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_MAIL_RCPT_ALLLOWFAILS 3 "16 Jan 2020" "libcurl 7.69.0" "curl_easy_setopt options"
+.SH NAME
+CURLOPT_MAIL_RCPT_ALLLOWFAILS \- allow RCPT TO command to fail for some recipients
+.SH SYNOPSIS
+.nf
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MAIL_RCPT_ALLLOWFAILS,
+                          long allow);
+.SH DESCRIPTION
+If \fIallow\fP is set to 1L, allow RCPT TO command to fail for some recipients.
+
+When sending data to multiple recipients, by default curl will abort SMTP
+conversation if at least one of the recipients causes RCPT TO command to
+return an error.
+
+The default behavior can be changed by setting \fIignore\fP to 1L which will
+make curl ignore errors and proceed with the remaining valid recipients.
+
+In case when all recipients cause RCPT TO command to fail, curl will abort SMTP
+conversation and return the error received from to the last RCPT TO command.
+.SH DEFAULT
+0
+.SH PROTOCOLS
+SMTP
+.SH EXAMPLE
+.nf
+CURL *curl = curl_easy_init();
+if(curl) {
+  struct curl_slist *list;
+
+  /* Adding one valid and one invalid email address */
+  list = curl_slist_append(NULL, "person@example.com");
+  list = curl_slist_append(list, "invalidemailaddress");
+
+  curl_easy_setopt(curl, CURLOPT_URL, "smtp://example.com/");
+  curl_easy_setopt(curl, CURLOPT_MAIL_RCPT_ALLLOWFAILS, 1L);
+
+  ret = curl_easy_perform(curl);
+  curl_slist_free_all(list);
+  curl_easy_cleanup(curl);
+}
+.fi
+.SH AVAILABILITY
+Added in 7.69.0.
+.SH RETURN VALUE
+Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
+.SH "SEE ALSO"
+.BR CURLOPT_MAIL_FROM "(3), " CURLOPT_MAIL_RCPT "(3), "
diff --git a/docs/libcurl/opts/Makefile.inc b/docs/libcurl/opts/Makefile.inc
index 93c4357d2..52bf422f4 100644
--- a/docs/libcurl/opts/Makefile.inc
+++ b/docs/libcurl/opts/Makefile.inc
@@ -188,6 +188,7 @@ man_MANS =                                      \
   CURLOPT_MAIL_AUTH.3                           \
   CURLOPT_MAIL_FROM.3                           \
   CURLOPT_MAIL_RCPT.3                           \
+  CURLOPT_MAIL_RCPT_ALLLOWFAILS.3               \
   CURLOPT_MAXAGE_CONN.3                         \
   CURLOPT_MAXCONNECTS.3                         \
   CURLOPT_MAXFILESIZE.3                         \
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index 711d5694b..07847f28b 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -471,6 +471,7 @@ CURLOPT_LOW_SPEED_TIME          7.1
 CURLOPT_MAIL_AUTH               7.25.0
 CURLOPT_MAIL_FROM               7.20.0
 CURLOPT_MAIL_RCPT               7.20.0
+CURLOPT_MAIL_RCPT_ALLLOWFAILS   7.69.0
 CURLOPT_MAXAGE_CONN             7.65.0
 CURLOPT_MAXCONNECTS             7.7
 CURLOPT_MAXFILESIZE             7.10.8