examples: Synchronised comments between SMTP MAIL examples

1 files changed, 9 insertions, 4 deletions

diff --git a/docs/examples/smtp-tls.c b/docs/examples/smtp-tls.c
index 4e610d9ac..4872dbdf1 100644
--- a/docs/examples/smtp-tls.c
+++ b/docs/examples/smtp-tls.c
@@ -117,7 +117,12 @@ int main(void)
      * docs/SSLCERTS for more information. */
     curl_easy_setopt(curl, CURLOPT_CAINFO, "/path/to/certificate.pem");
 
-    /* Value for envelope reverse-path */
+    /* Note that this option isn't strictly required, omitting it will result in
+     * libcurl sending the MAIL FROM command with empty sender data. All
+     * autoresponses should have an empty reverse-path, and should be directed
+     * to the address in the reverse-path which triggered them. Otherwise, they
+     * could cause an endless loop. See RFC 5321 Section 4.5.5 for more details.
+     */
     curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM);
 
     /* Add two recipients, in this particular case they correspond to the
@@ -127,9 +132,9 @@ int main(void)
     recipients = curl_slist_append(recipients, CC);
     curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
 
-    /* In this case, we're using a callback function to specify the data. You
-     * could just use the CURLOPT_READDATA option to specify a FILE pointer to
-     * read from. */
+    /* We're using a callback function to specify the payload (the headers and
+     * body of the message). You could just use the CURLOPT_READDATA option to
+     * specify a FILE pointer to read from. */
     curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
     curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);
     curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);