diff --git a/cmd/serve.go b/cmd/serve.go
index f869cd46..c799f5a6 100644
--- a/cmd/serve.go
+++ b/cmd/serve.go
@@ -177,8 +177,8 @@ func execServe(c *cli.Context) error {
 		return errors.New("if set, certificate file must exist")
 	} else if listenHTTPS != "" && (keyFile == "" || certFile == "") {
 		return errors.New("if listen-https is set, both key-file and cert-file must be set")
-	} else if smtpSenderAddr != "" && (baseURL == "" || smtpSenderUser == "" || smtpSenderPass == "" || smtpSenderFrom == "") {
-		return errors.New("if smtp-sender-addr is set, base-url, smtp-sender-user, smtp-sender-pass and smtp-sender-from must also be set")
+	} else if smtpSenderAddr != "" && (baseURL == "" || smtpSenderFrom == "") {
+		return errors.New("if smtp-sender-addr is set, base-url, and smtp-sender-from must also be set")
 	} else if smtpServerListen != "" && smtpServerDomain == "" {
 		return errors.New("if smtp-server-listen is set, smtp-server-domain must also be set")
 	} else if attachmentCacheDir != "" && baseURL == "" {
diff --git a/docs/releases.md b/docs/releases.md
index 4212f6d1..2ae03ca6 100644
--- a/docs/releases.md
+++ b/docs/releases.md
@@ -2,6 +2,12 @@
 Binaries for all releases can be found on the GitHub releases pages for the [ntfy server](https://github.com/binwiederhier/ntfy/releases)
 and the [ntfy Android app](https://github.com/binwiederhier/ntfy-android/releases).
 
+## ntfy server v2.2.0 (UNRELEASED)
+
+**Features:**
+
+* Support SMTP servers without auth ([#645](https://github.com/binwiederhier/ntfy/issues/645), thanks to [@Sharknoon](https://github.com/Sharknoon) for reporting)
+
 ## ntfy server v2.1.1
 Released March 1, 2023
 
diff --git a/server/log.go b/server/log.go
index 8e521283..643f2ccb 100644
--- a/server/log.go
+++ b/server/log.go
@@ -31,7 +31,7 @@ const (
 )
 
 var (
-	normalErrorCodes       = []int{http.StatusNotFound, http.StatusBadRequest, http.StatusTooManyRequests, http.StatusUnauthorized, http.StatusInsufficientStorage}
+	normalErrorCodes       = []int{http.StatusNotFound, http.StatusBadRequest, http.StatusTooManyRequests, http.StatusUnauthorized, http.StatusForbidden, http.StatusInsufficientStorage}
 	rateLimitingErrorCodes = []int{http.StatusTooManyRequests, http.StatusRequestEntityTooLarge}
 )
 
diff --git a/server/server.yml b/server/server.yml
index cb50633b..5c7955dd 100644
--- a/server/server.yml
+++ b/server/server.yml
@@ -117,18 +117,19 @@
 # attachment-expiry-duration: "3h"
 
 # If enabled, allow outgoing e-mail notifications via the 'X-Email' header. If this header is set,
-# messages will additionally be sent out as e-mail using an external SMTP server. As of today, only
-# SMTP servers with plain text auth and STARTLS are supported. Please also refer to the rate limiting settings
-# below (visitor-email-limit-burst & visitor-email-limit-burst).
+# messages will additionally be sent out as e-mail using an external SMTP server.
+#
+# As of today, only SMTP servers with plain text auth (or no auth at all), and STARTLS are supported.
+# Please also refer to the rate limiting settings below (visitor-email-limit-burst & visitor-email-limit-burst).
 #
 # - smtp-sender-addr is the hostname:port of the SMTP server
-# - smtp-sender-user/smtp-sender-pass are the username and password of the SMTP user
 # - smtp-sender-from is the e-mail address of the sender
+# - smtp-sender-user/smtp-sender-pass are the username and password of the SMTP user (leave blank for no auth)
 #
 # smtp-sender-addr:
+# smtp-sender-from:
 # smtp-sender-user:
 # smtp-sender-pass:
-# smtp-sender-from:
 
 # If enabled, ntfy will launch a lightweight SMTP server for incoming messages. Once configured, users can send
 # emails to a topic e-mail address to publish messages to a topic.
diff --git a/server/smtp_sender.go b/server/smtp_sender.go
index ee263658..26a0e0e6 100644
--- a/server/smtp_sender.go
+++ b/server/smtp_sender.go
@@ -36,7 +36,10 @@ func (s *smtpSender) Send(v *visitor, m *message, to string) error {
 		if err != nil {
 			return err
 		}
-		auth := smtp.PlainAuth("", s.config.SMTPSenderUser, s.config.SMTPSenderPass, host)
+		var auth smtp.Auth
+		if s.config.SMTPSenderUser != "" {
+			auth = smtp.PlainAuth("", s.config.SMTPSenderUser, s.config.SMTPSenderPass, host)
+		}
 		ev := logvm(v, m).
 			Tag(tagEmail).
 			Fields(log.Context{