diff --git a/smtp/address.go b/smtp/address.go
index f25f378..ad23d92 100644
--- a/smtp/address.go
+++ b/smtp/address.go
@@ -102,11 +102,17 @@ func (a Address) IsZero() bool {
 // formatted with non-ASCII characters. If localpart has non-ASCII characters,
 // they are returned regardless of smtputf8.
 func (a Address) Pack(smtputf8 bool) string {
+	if a.IsZero() {
+		return ""
+	}
 	return a.Localpart.String() + "@" + a.Domain.XName(smtputf8)
 }
 
 // String returns the address in string form with non-ASCII characters.
 func (a Address) String() string {
+	if a.IsZero() {
+		return ""
+	}
 	return a.Localpart.String() + "@" + a.Domain.Name()
 }
 
diff --git a/smtpserver/server.go b/smtpserver/server.go
index 753683d..000e890 100644
--- a/smtpserver/server.go
+++ b/smtpserver/server.go
@@ -2193,7 +2193,7 @@ func (c *conn) deliver(ctx context.Context, recvHdrFor func(string) string, msgW
 				}
 			}
 
-			log.Info("incoming message rejected", mlog.Field("reason", a.reason))
+			log.Info("incoming message rejected", mlog.Field("reason", a.reason), mlog.Field("msgfrom", msgFrom))
 			metricDelivery.WithLabelValues("reject", a.reason).Inc()
 			c.setSlow(true)
 			addError(rcptAcc, a.code, a.secode, a.userError, a.errmsg)