From 32d0206af0e752d7d68db460ca9e089af15dc59a Mon Sep 17 00:00:00 2001
From: Mark Gardner <mark@outer-limit.com>
Date: Thu, 21 Apr 2022 11:29:15 -0500
Subject: [PATCH] throw an error if the remote is configured for starttls and
 the server does not have the extension

---
 smtp.go | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/smtp.go b/smtp.go
index e5bdd69..14ab8c1 100644
--- a/smtp.go
+++ b/smtp.go
@@ -374,6 +374,8 @@ func SendMail(r *Remote, from string, to []string, msg []byte) error {
 			if err = c.StartTLS(config); err != nil {
 				return err
 			}
+		} else if r.Scheme == "starttls" {
+			return errors.New("starttls: server does not support extension, check remote scheme")
 		}
 	}
 	if r.Auth != nil && c.ext != nil {