1 /***************************************************************************
2 * _ _ ____ _
3 * Project ___| | | | _ \| |
4 * / __| | | | |_) | |
5 * | (__| |_| | _ <| |___
6 * \___|\___/|_| \_\_____|
7 *
8 * Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
9 *
10 * This software is licensed as described in the file COPYING, which
11 * you should have received as part of this distribution. The terms
12 * are also available at https://curl.se/docs/copyright.html.
13 *
14 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
15 * copies of the Software, and permit persons to whom the Software is
16 * furnished to do so, under the terms of the COPYING file.
17 *
18 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
19 * KIND, either express or implied.
20 *
21 * SPDX-License-Identifier: curl
22 *
23 ***************************************************************************/
24
25 /* <DESC>
26 * Send SMTP email using implicit TLS
27 * </DESC>
28 */
29
30 #include <stdio.h>
31 #include <string.h>
32 #include <curl/curl.h>
33
34 /* This is a simple example showing how to send mail using libcurl's SMTP
35 * capabilities. It builds on the smtp-mail.c example to add authentication
36 * and, more importantly, transport security to protect the authentication
37 * details from being snooped.
38 *
39 * Note that this example requires libcurl 7.20.0 or above.
40 */
41
42 #define FROM_MAIL "<sender@example.com>"
43 #define TO_MAIL "<recipient@example.com>"
44 #define CC_MAIL "<info@example.com>"
45
46 static const char *payload_text =
47 "Date: Mon, 29 Nov 2010 21:54:29 +1100\r\n"
48 "To: " TO_MAIL "\r\n"
49 "From: " FROM_MAIL "\r\n"
50 "Cc: " CC_MAIL "\r\n"
51 "Message-ID: <dcd7cb36-11db-487a-9f3a-e652a9458efd@"
52 "rfcpedant.example.org>\r\n"
53 "Subject: SMTP example message\r\n"
54 "\r\n" /* empty line to divide headers from body, see RFC 5322 */
55 "The body of the message starts here.\r\n"
56 "\r\n"
57 "It could be a lot of lines, could be MIME encoded, whatever.\r\n"
58 "Check RFC 5322.\r\n";
59
60 struct upload_status {
61 size_t bytes_read;
62 };
63
payload_source(char * ptr,size_t size,size_t nmemb,void * userp)64 static size_t payload_source(char *ptr, size_t size, size_t nmemb, void *userp)
65 {
66 struct upload_status *upload_ctx = (struct upload_status *)userp;
67 const char *data;
68 size_t room = size * nmemb;
69
70 if((size == 0) || (nmemb == 0) || ((size*nmemb) < 1)) {
71 return 0;
72 }
73
74 data = &payload_text[upload_ctx->bytes_read];
75
76 if(data) {
77 size_t len = strlen(data);
78 if(room < len)
79 len = room;
80 memcpy(ptr, data, len);
81 upload_ctx->bytes_read += len;
82
83 return len;
84 }
85
86 return 0;
87 }
88
main(void)89 int main(void)
90 {
91 CURL *curl;
92 CURLcode res = CURLE_OK;
93 struct curl_slist *recipients = NULL;
94 struct upload_status upload_ctx = { 0 };
95
96 curl = curl_easy_init();
97 if(curl) {
98 /* Set username and password */
99 curl_easy_setopt(curl, CURLOPT_USERNAME, "user");
100 curl_easy_setopt(curl, CURLOPT_PASSWORD, "secret");
101
102 /* This is the URL for your mailserver. Note the use of port 587 here,
103 * instead of the normal SMTP port (25). Port 587 is commonly used for
104 * secure mail submission (see RFC 4403), but you should use whatever
105 * matches your server configuration. */
106 curl_easy_setopt(curl, CURLOPT_URL, "smtp://mainserver.example.net:587");
107
108 /* In this example, we start with a plain text connection, and upgrade to
109 * Transport Layer Security (TLS) using the STARTTLS command. Be careful
110 * of using CURLUSESSL_TRY here, because if TLS upgrade fails, the
111 * transfer continues anyway - see the security discussion in the libcurl
112 * tutorial for more details. */
113 curl_easy_setopt(curl, CURLOPT_USE_SSL, (long)CURLUSESSL_ALL);
114
115 /* If your server does not have a valid certificate, then you can disable
116 * part of the Transport Layer Security protection by setting the
117 * CURLOPT_SSL_VERIFYPEER and CURLOPT_SSL_VERIFYHOST options to 0 (false).
118 * curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
119 * curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
120 * That is, in general, a bad idea. It is still better than sending your
121 * authentication details in plain text though. Instead, you should get
122 * the issuer certificate (or the host certificate if the certificate is
123 * self-signed) and add it to the set of certificates that are known to
124 * libcurl using CURLOPT_CAINFO and/or CURLOPT_CAPATH. See docs/SSLCERTS
125 * for more information. */
126 curl_easy_setopt(curl, CURLOPT_CAINFO, "/path/to/certificate.pem");
127
128 /* Note that this option is not strictly required, omitting it results in
129 * libcurl sending the MAIL FROM command with empty sender data. All
130 * autoresponses should have an empty reverse-path, and should be directed
131 * to the address in the reverse-path which triggered them. Otherwise,
132 * they could cause an endless loop. See RFC 5321 Section 4.5.5 for more
133 * details.
134 */
135 curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM_MAIL);
136
137 /* Add two recipients, in this particular case they correspond to the
138 * To: and Cc: addressees in the header, but they could be any kind of
139 * recipient. */
140 recipients = curl_slist_append(recipients, TO_MAIL);
141 recipients = curl_slist_append(recipients, CC_MAIL);
142 curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
143
144 /* We are using a callback function to specify the payload (the headers and
145 * body of the message). You could just use the CURLOPT_READDATA option to
146 * specify a FILE pointer to read from. */
147 curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
148 curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);
149 curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
150
151 /* Since the traffic is encrypted, it is useful to turn on debug
152 * information within libcurl to see what is happening during the
153 * transfer.
154 */
155 curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
156
157 /* Send the message */
158 res = curl_easy_perform(curl);
159
160 /* Check for errors */
161 if(res != CURLE_OK)
162 fprintf(stderr, "curl_easy_perform() failed: %s\n",
163 curl_easy_strerror(res));
164
165 /* Free the list of recipients */
166 curl_slist_free_all(recipients);
167
168 /* Always cleanup */
169 curl_easy_cleanup(curl);
170 }
171
172 return (int)res;
173 }
174
