diff --git a/lib/smtp.c b/lib/smtp.c
index cdeeb7a265..ef51c829ab 100644
--- a/lib/smtp.c
+++ b/lib/smtp.c
@@ -670,6 +670,23 @@ static CURLcode smtp_perform_mail(struct connectdata *conn)
     }
   }
 
+  /* If the mailboxes in the FROM and AUTH parameters don't include a UTF-8
+     based address then quickly scan through the recipient list and check if
+     any there do, as we need to correctly identify our support for SMTPUTF8
+     in the envelope, as per RFC-6531 sect. 3.4 */
+  if(conn->proto.smtpc.utf8_supported && !utf8) {
+    struct SMTP *smtp = data->req.protop;
+    struct curl_slist *rcpt = smtp->rcpt;
+
+    while(rcpt && !utf8) {
+      /* Does the host name contain non-ASCII characters? */
+      if(!Curl_is_ASCII_name(rcpt->data))
+        utf8 = TRUE;
+
+      rcpt = rcpt->next;
+    }
+  }
+
   /* Send the MAIL command */
   result = Curl_pp_sendf(&conn->proto.smtpc.pp,
                          "MAIL FROM:%s%s%s%s%s%s",
@@ -679,7 +696,7 @@ static CURLcode smtp_perform_mail(struct connectdata *conn)
                          size ? " SIZE=" : "", /* Optional on SIZE support  */
                          size ? size : "",     /*                           */
                          utf8 ? " SMTPUTF8"    /* Internationalised mailbox */
-                               : "");          /* address included          */
+                               : "");          /* included in our envelope  */
 
   free(from);
   free(auth);
diff --git a/tests/data/Makefile.inc b/tests/data/Makefile.inc
index 4ddfeef36c..2a75cffdbe 100644
--- a/tests/data/Makefile.inc
+++ b/tests/data/Makefile.inc
@@ -109,7 +109,7 @@ test927 test928 test929 test930 test931 test932 test933 test934 test935 \
 test936 test937 test938 test939 test940 test941 test942 test943 test944 \
 test945 test946 test947 test948 test949 test950 test951 test952 test953 \
 test954 test955 test956 test957 test958 test959 test960 test961 test962 \
-test963 test964 test965 \
+test963 test964 test965 test966 \
 \
 test1000 test1001 test1002 test1003 test1004 test1005 test1006 test1007 \
 test1008 test1009 test1010 test1011 test1012 test1013 test1014 test1015 \
diff --git a/tests/data/test966 b/tests/data/test966
new file mode 100644
index 0000000000..6dc839aba7
--- /dev/null
+++ b/tests/data/test966
@@ -0,0 +1,65 @@
+<testcase>
+<info>
+<keywords>
+SMTP
+IDN
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<servercmd>
+CAPA SMTPUTF8
+</servercmd>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+smtp
+</server>
+<features>
+idn
+</features>
+<setenv>
+LC_ALL=en_US.UTF-8
+LC_CTYPE=en_US.UTF-8
+</setenv>
+<precheck>
+perl -MI18N::Langinfo=langinfo,CODESET -e 'die "Needs a UTF-8 locale" if (lc(langinfo(CODESET())) ne "utf-8");'
+</precheck>
+ <name>
+SMTP with SMTPUTF8 support - UTF-8 based recipient
+ </name>
+<stdin>
+From: different
+To: another
+
+body
+</stdin>
+<command>
+smtp://%HOSTIP:%SMTPPORT/966 --mail-rcpt Stödmottagaren@åäö.se --mail-from sender@example.com -T -
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<protocol>
+EHLO 966
+MAIL FROM:<sender@example.com> SMTPUTF8
+RCPT TO:<Stödmottagaren@xn--4cab6c.se>
+DATA
+QUIT
+</protocol>
+<upload>
+From: different
+To: another
+
+body
+.
+</upload>
+</verify>
+</testcase>
diff --git a/tests/ftpserver.pl b/tests/ftpserver.pl
index fe74f8b078..9c4b88aeff 100755
--- a/tests/ftpserver.pl
+++ b/tests/ftpserver.pl
@@ -871,16 +871,19 @@ sub RCPT_smtp {
         sendcontrol "501 Unrecognized parameter\r\n";
     }
     else {
+        my $smtputf8 = grep /^SMTPUTF8$/, @capabilities;
         my $to = $1;
 
         # Validate the to address (only a valid email address inside <> is
         # allowed, such as <user@example.com>)
-        if ($to !~
-            /^<([a-zA-Z0-9._%+-]+)\@(([a-zA-Z0-9-]+)\.)+([a-zA-Z]{2,4})>$/) {
-            sendcontrol "501 Invalid address\r\n";
+        if ((!$smtputf8 && $to =~
+              /^<([a-zA-Z0-9._%+-]+)\@(([a-zA-Z0-9-]+)\.)+([a-zA-Z]{2,4})>$/) ||
+            ($smtputf8 && $to =~
+              /^<([a-zA-Z0-9\x{80}-\x{ff}._%+-]+)\@(([a-zA-Z0-9\x{80}-\x{ff}-]+)\.)+([a-zA-Z]{2,4})>$/)) {
+            sendcontrol "250 Recipient OK\r\n";      
         }
         else {
-            sendcontrol "250 Recipient OK\r\n";
+            sendcontrol "501 Invalid address\r\n";
         }
     }