SMTP: only send SIZE if supported

SMTP client will send SIZE parameter in MAIL FROM command only if server
supports it. Without this patch server might say "504 Command parameter
not implemented" and reject the message.

Bug: http://curl.haxx.se/bug/view.cgi?id=3564114

2 files changed, 8 insertions, 1 deletions

diff --git a/lib/smtp.c b/lib/smtp.c
index 81c069f7d..b73bb2d89 100644
--- a/lib/smtp.c
+++ b/lib/smtp.c
@@ -232,6 +232,11 @@ static int smtp_endofresp(struct pingpong *pp, int *resp)
   line += 4;
   len -= 4;
 
+  if(smtpc->state == SMTP_EHLO && len >= 4 && !memcmp(line, "SIZE", 4)) {
+    DEBUGF(infof(conn->data, "Server supports SIZE extension.\n"));
+    smtpc->size_supported = true;
+  }
+
   if(smtpc->state == SMTP_EHLO && len >= 5 && !memcmp(line, "AUTH ", 5)) {
     line += 5;
     len -= 5;
@@ -943,7 +948,7 @@ static CURLcode smtp_mail(struct connectdata *conn)
   }
 
   /* calculate the optional SIZE parameter */
-  if(conn->data->set.infilesize > 0) {
+  if(conn->proto.smtpc.size_supported && conn->data->set.infilesize > 0) {
     size = aprintf("%" FORMAT_OFF_T, data->set.infilesize);
 
     if(!size) {
diff --git a/lib/smtp.h b/lib/smtp.h
index 38fd1b70a..d68a659b5 100644
--- a/lib/smtp.h
+++ b/lib/smtp.h
@@ -66,6 +66,8 @@ struct smtp_conn {
   struct curl_slist *rcpt; /* Recipient list */
   bool ssldone;            /* Is connect() over SSL done? only relevant in
                               multi mode */
+  bool size_supported;     /* If server supports SIZE extension according to
+                              RFC 1870 */
 };
 
 extern const struct Curl_handler Curl_handler_smtp;