diff -ru OpenSMTPD-opensmtpd-6.0.3/smtpd/mta_session.c OpenSMTPD-opensmtpd-6.0.3-fixed/smtpd/mta_session.c
--- OpenSMTPD-opensmtpd-6.0.3/smtpd/mta_session.c	2018-01-04 23:24:01.000000000 +0100
+++ OpenSMTPD-opensmtpd-6.0.3-fixed/smtpd/mta_session.c	2020-01-29 09:47:24.607457717 +0100
@@ -1290,40 +1290,20 @@
 		break;
 
 	case IO_ERROR:
+	case IO_TLSERROR:
 		log_debug("debug: mta: %p: IO error: %s", s, io_error(io));
-		if (!s->ready) {
-			mta_error(s, "IO Error: %s", io_error(io));
-			mta_connect(s);
-			break;
-		}
-		else if (!(s->flags & (MTA_FORCE_TLS|MTA_FORCE_SMTPS|MTA_FORCE_ANYSSL))) {
-			/* error in non-strict SSL negotiation, downgrade to plain */
-			if (s->flags & MTA_TLS) {
-				log_info("smtp-out: Error on session %016"PRIx64
-				    ": opportunistic TLS failed, "
-				    "downgrading to plain", s->id);
-				s->flags &= ~MTA_TLS;
-				s->flags |= MTA_DOWNGRADE_PLAIN;
-				mta_connect(s);
-				break;
-			}
-		}
-		mta_error(s, "IO Error: %s", io_error(io));
-		mta_free(s);
-		break;
 
-	case IO_TLSERROR:
-		log_debug("debug: mta: %p: TLS IO error: %s", s, io_error(io));
-		if (!(s->flags & (MTA_FORCE_TLS|MTA_FORCE_SMTPS|MTA_FORCE_ANYSSL))) {
+		if (s->state == MTA_STARTTLS && s->use_smtp_tls) {
 			/* error in non-strict SSL negotiation, downgrade to plain */
-			log_info("smtp-out: TLS Error on session %016"PRIx64
-			    ": TLS failed, "
+			log_info("smtp-out: Error on session %016"PRIx64
+			    ": opportunistic TLS failed, "
 			    "downgrading to plain", s->id);
 			s->flags &= ~MTA_TLS;
 			s->flags |= MTA_DOWNGRADE_PLAIN;
 			mta_connect(s);
 			break;
 		}
+
 		mta_error(s, "IO Error: %s", io_error(io));
 		mta_free(s);
 		break;
diff -ru OpenSMTPD-opensmtpd-6.0.3/smtpd/smtp_session.c OpenSMTPD-opensmtpd-6.0.3-fixed/smtpd/smtp_session.c
--- OpenSMTPD-opensmtpd-6.0.3/smtpd/smtp_session.c	2018-01-04 23:24:01.000000000 +0100
+++ OpenSMTPD-opensmtpd-6.0.3-fixed/smtpd/smtp_session.c	2020-01-29 09:47:24.610791335 +0100
@@ -2004,25 +2004,23 @@
 		memmove(maddr->user, p, strlen(p) + 1);
 	}
 
-	if (!valid_localpart(maddr->user) ||
-	    !valid_domainpart(maddr->domain)) {
-		/* accept empty return-path in MAIL FROM, required for bounces */
-		if (mailfrom && maddr->user[0] == '\0' && maddr->domain[0] == '\0')
-			return (1);
+	/* accept empty return-path in MAIL FROM, required for bounces */
+	if (mailfrom && maddr->user[0] == '\0' && maddr->domain[0] == '\0')
+		return (1);
 
-		/* no user-part, reject */
-		if (maddr->user[0] == '\0')
-			return (0);
-
-		/* no domain, local user */
-		if (maddr->domain[0] == '\0') {
-			(void)strlcpy(maddr->domain, domain,
-			    sizeof(maddr->domain));
-			return (1);
-		}
+	/* no or invalid user-part, reject */
+	if (maddr->user[0] == '\0' || !valid_localpart(maddr->user))
 		return (0);
+
+	/* no domain part, local user */
+	if (maddr->domain[0] == '\0') {
+		(void)strlcpy(maddr->domain, domain,
+			sizeof(maddr->domain));
 	}
 
+	if (!valid_domainpart(maddr->domain))
+		return (0);
+
 	return (1);
 }
 
diff -ru opensmtpd-6.0.3p1/smtpd/mta_session.c opensmtpd-6.0.3p1-modified/smtpd/mta_session.c
--- opensmtpd-6.0.3p1/smtpd/mta_session.c	2018-01-10 21:06:40.000000000 +0800
+++ opensmtpd-6.0.3p1-modified/smtpd/mta_session.c	2020-02-25 09:57:04.624147227 +0800
@@ -1214,7 +1214,7 @@
 		if (cont) {
 			if (s->replybuf[0] == '\0')
 				(void)strlcat(s->replybuf, line, sizeof s->replybuf);
-			else {
+			else if (len > 4) {
 				line = line + 4;
 				if (isdigit((int)*line) && *(line + 1) == '.' &&
 				    isdigit((int)*line+2) && *(line + 3) == '.' &&
@@ -1229,7 +1229,9 @@
 		/* last line of a reply, check if we're on a continuation to parse out status and ESC.
 		 * if we overflow reply buffer or are not on continuation, log entire last line.
 		 */
-		if (s->replybuf[0] != '\0') {
+		if (s->replybuf[0] == '\0')
+			(void)strlcat(s->replybuf, line, sizeof s->replybuf);
+		else if (len > 4) {
 			p = line + 4;
 			if (isdigit((int)*p) && *(p + 1) == '.' &&
 			    isdigit((int)*p+2) && *(p + 3) == '.' &&
@@ -1238,8 +1240,6 @@
 			if (strlcat(s->replybuf, p, sizeof s->replybuf) >= sizeof s->replybuf)
 				(void)strlcpy(s->replybuf, line, sizeof s->replybuf);
 		}
-		else
-			(void)strlcpy(s->replybuf, line, sizeof s->replybuf);
 
 		if (s->state == MTA_QUIT) {
 			log_info("%016"PRIx64" mta event=closed reason=quit messages=%zu",