diff --git a/cmd/serve.go b/cmd/serve.go
index 550e26a0..83a5b838 100644
--- a/cmd/serve.go
+++ b/cmd/serve.go
@@ -26,6 +26,9 @@ var flagsServe = []cli.Flag{
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-user", EnvVars: []string{"NTFY_SMTP_USER"}, Usage: "SMTP user (if e-mail sending is enabled)"}),
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-pass", EnvVars: []string{"NTFY_SMTP_PASS"}, Usage: "SMTP password (if e-mail sending is enabled)"}),
 	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-from", EnvVars: []string{"NTFY_SMTP_FROM"}, Usage: "SMTP sender address (if e-mail sending is enabled)"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-server-listen", EnvVars: []string{"NTFY_SMTP_SERVER_LISTEN"}, Usage: "xxxxxxxxxx"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-server-domain", EnvVars: []string{"NTFY_SMTP_SERVER_DOMAIN"}, Usage: "xxxxxxxxxxx"}),
+	altsrc.NewStringFlag(&cli.StringFlag{Name: "smtp-server-addr-prefix", EnvVars: []string{"NTFY_SMTP_SERVER_ADDR_PREFIX"}, Usage: "xxxxxxxxxxx"}),
 	altsrc.NewIntFlag(&cli.IntFlag{Name: "global-topic-limit", Aliases: []string{"T"}, EnvVars: []string{"NTFY_GLOBAL_TOPIC_LIMIT"}, Value: server.DefaultGlobalTopicLimit, Usage: "total number of topics allowed"}),
 	altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-subscription-limit", EnvVars: []string{"NTFY_VISITOR_SUBSCRIPTION_LIMIT"}, Value: server.DefaultVisitorSubscriptionLimit, Usage: "number of subscriptions per visitor"}),
 	altsrc.NewIntFlag(&cli.IntFlag{Name: "visitor-request-limit-burst", EnvVars: []string{"NTFY_VISITOR_REQUEST_LIMIT_BURST"}, Value: server.DefaultVisitorRequestLimitBurst, Usage: "initial limit of requests per visitor"}),
@@ -68,10 +71,13 @@ func execServe(c *cli.Context) error {
 	cacheDuration := c.Duration("cache-duration")
 	keepaliveInterval := c.Duration("keepalive-interval")
 	managerInterval := c.Duration("manager-interval")
-	smtpAddr := c.String("smtp-addr")
-	smtpUser := c.String("smtp-user")
-	smtpPass := c.String("smtp-pass")
-	smtpFrom := c.String("smtp-from")
+	smtpSenderAddr := c.String("smtp-addr")
+	smtpSenderUser := c.String("smtp-user")
+	smtpSenderPass := c.String("smtp-pass")
+	smtpSenderFrom := c.String("smtp-from")
+	smtpServerListen := c.String("smtp-server-listen")
+	smtpServerDomain := c.String("smtp-server-domain")
+	smtpServerAddrPrefix := c.String("smtp-server-addr-prefix")
 	globalTopicLimit := c.Int("global-topic-limit")
 	visitorSubscriptionLimit := c.Int("visitor-subscription-limit")
 	visitorRequestLimitBurst := c.Int("visitor-request-limit-burst")
@@ -95,7 +101,7 @@ 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 smtpAddr != "" && (baseURL == "" || smtpUser == "" || smtpPass == "" || smtpFrom == "") {
+	} else if smtpSenderAddr != "" && (baseURL == "" || smtpSenderUser == "" || smtpSenderPass == "" || smtpSenderFrom == "") {
 		return errors.New("if smtp-addr is set, base-url, smtp-user, smtp-pass and smtp-from must also be set")
 	}
 
@@ -111,10 +117,13 @@ func execServe(c *cli.Context) error {
 	conf.CacheDuration = cacheDuration
 	conf.KeepaliveInterval = keepaliveInterval
 	conf.ManagerInterval = managerInterval
-	conf.SMTPAddr = smtpAddr
-	conf.SMTPUser = smtpUser
-	conf.SMTPPass = smtpPass
-	conf.SMTPFrom = smtpFrom
+	conf.SMTPSenderAddr = smtpSenderAddr
+	conf.SMTPSenderUser = smtpSenderUser
+	conf.SMTPSenderPass = smtpSenderPass
+	conf.SMTPSenderFrom = smtpSenderFrom
+	conf.SMTPServerListen = smtpServerListen
+	conf.SMTPServerDomain = smtpServerDomain
+	conf.SMTPServerAddrPrefix = smtpServerAddrPrefix
 	conf.GlobalTopicLimit = globalTopicLimit
 	conf.VisitorSubscriptionLimit = visitorSubscriptionLimit
 	conf.VisitorRequestLimitBurst = visitorRequestLimitBurst
diff --git a/server/config.go b/server/config.go
index b127d64d..b5422baa 100644
--- a/server/config.go
+++ b/server/config.go
@@ -45,10 +45,13 @@ type Config struct {
 	ManagerInterval              time.Duration
 	AtSenderInterval             time.Duration
 	FirebaseKeepaliveInterval    time.Duration
-	SMTPAddr                     string
-	SMTPUser                     string
-	SMTPPass                     string
-	SMTPFrom                     string
+	SMTPSenderAddr               string
+	SMTPSenderUser               string
+	SMTPSenderPass               string
+	SMTPSenderFrom               string
+	SMTPServerListen             string
+	SMTPServerDomain             string
+	SMTPServerAddrPrefix         string
 	MessageLimit                 int
 	MinDelay                     time.Duration
 	MaxDelay                     time.Duration
diff --git a/server/mailserver.go b/server/mailserver.go
deleted file mode 100644
index 08f2c193..00000000
--- a/server/mailserver.go
+++ /dev/null
@@ -1,102 +0,0 @@
-package server
-
-import (
-	"bytes"
-	"errors"
-	"fmt"
-	"github.com/emersion/go-smtp"
-	"io"
-	"io/ioutil"
-	"log"
-	"net/http"
-	"net/http/httptest"
-	"net/mail"
-	"strings"
-	"sync"
-)
-
-// mailBackend implements SMTP server methods.
-type mailBackend struct {
-	s *Server
-}
-
-func (b *mailBackend) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) {
-	return &Session{s: b.s}, nil
-}
-
-func (b *mailBackend) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) {
-	return &Session{s: b.s}, nil
-}
-
-// Session is returned after EHLO.
-type Session struct {
-	s        *Server
-	from, to string
-	mu       sync.Mutex
-}
-
-func (s *Session) AuthPlain(username, password string) error {
-	return nil
-}
-
-func (s *Session) Mail(from string, opts smtp.MailOptions) error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	s.from = from
-	log.Println("Mail from:", from)
-	return nil
-}
-
-func (s *Session) Rcpt(to string) error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	s.to = to
-	log.Println("Rcpt to:", to)
-	return nil
-}
-
-func (s *Session) Data(r io.Reader) error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	b, err := ioutil.ReadAll(r)
-	if err != nil {
-		return err
-	}
-
-	log.Println("Data:", string(b))
-	msg, err := mail.ReadMessage(bytes.NewReader(b))
-	if err != nil {
-		return err
-	}
-	body, err := io.ReadAll(msg.Body)
-	if err != nil {
-		return err
-	}
-	topic := strings.TrimSuffix(s.to, "@ntfy.sh")
-	url := fmt.Sprintf("%s/%s", s.s.config.BaseURL, topic)
-	req, err := http.NewRequest("PUT", url, bytes.NewReader(body))
-	if err != nil {
-		return err
-	}
-	subject := msg.Header.Get("Subject")
-	if subject != "" {
-		req.Header.Set("Title", subject)
-	}
-	rr := httptest.NewRecorder()
-	s.s.handle(rr, req)
-	if rr.Code != http.StatusOK {
-		return errors.New("error: " + rr.Body.String())
-	}
-	return nil
-}
-
-func (s *Session) Reset() {
-	s.mu.Lock()
-	s.from = ""
-	s.to = ""
-	s.mu.Unlock()
-}
-
-func (s *Session) Logout() error {
-	return nil
-}
diff --git a/server/server.go b/server/server.go
index c2f8034b..6461085c 100644
--- a/server/server.go
+++ b/server/server.go
@@ -5,6 +5,7 @@ import (
 	"context"
 	"embed"
 	"encoding/json"
+	"errors"
 	firebase "firebase.google.com/go"
 	"firebase.google.com/go/messaging"
 	"fmt"
@@ -16,6 +17,7 @@ import (
 	"log"
 	"net"
 	"net/http"
+	"net/http/httptest"
 	"regexp"
 	"strconv"
 	"strings"
@@ -147,8 +149,8 @@ func New(conf *Config) (*Server, error) {
 		}
 	}
 	var mailer mailer
-	if conf.SMTPAddr != "" {
-		mailer = &smtpMailer{config: conf}
+	if conf.SMTPSenderAddr != "" {
+		mailer = &smtpSender{config: conf}
 	}
 	cache, err := createCache(conf)
 	if err != nil {
@@ -239,9 +241,9 @@ func (s *Server) Run() error {
 			errChan <- s.httpsServer.ListenAndServeTLS(s.config.CertFile, s.config.KeyFile)
 		}()
 	}
-	if true {
+	if s.config.SMTPServerListen != "" {
 		go func() {
-			errChan <- s.mailserver()
+			errChan <- s.runMailserver()
 		}()
 	}
 	s.mu.Unlock()
@@ -729,15 +731,31 @@ func (s *Server) updateStatsAndPrune() {
 		s.messages, len(s.topics), subscribers, messages, len(s.visitors))
 }
 
-func (s *Server) mailserver() error {
-	ms := smtp.NewServer(&mailBackend{s})
+func (s *Server) runMailserver() error {
+	sub := func(m *message) error {
+		url := fmt.Sprintf("%s/%s", s.config.BaseURL, m.Topic)
+		req, err := http.NewRequest("PUT", url, strings.NewReader(m.Message))
+		if err != nil {
+			return err
+		}
+		if m.Title != "" {
+			req.Header.Set("Title", m.Title)
+		}
+		rr := httptest.NewRecorder()
+		s.handle(rr, req)
+		if rr.Code != http.StatusOK {
+			return errors.New("error: " + rr.Body.String())
+		}
+		return nil
+	}
+	ms := smtp.NewServer(newMailBackend(s.config, sub))
 
-	ms.Addr = ":1025"
-	ms.Domain = "localhost"
+	ms.Addr = s.config.SMTPServerListen
+	ms.Domain = s.config.SMTPServerDomain
 	ms.ReadTimeout = 10 * time.Second
 	ms.WriteTimeout = 10 * time.Second
-	ms.MaxMessageBytes = 1024 * 1024
-	ms.MaxRecipients = 50
+	ms.MaxMessageBytes = 2 * s.config.MessageLimit
+	ms.MaxRecipients = 1
 	ms.AllowInsecureAuth = true
 
 	log.Println("Starting server at", ms.Addr)
diff --git a/server/server.yml b/server/server.yml
index 8f8930f3..e6afefc4 100644
--- a/server/server.yml
+++ b/server/server.yml
@@ -59,6 +59,9 @@
 # smtp-pass:
 # smtp-from:
 
+# smtp-server-listen:
+# smtp-server-addr:
+
 # Interval in which keepalive messages are sent to the client. This is to prevent
 # intermediaries closing the connection for inactivity.
 #
diff --git a/server/mailer.go b/server/smtp_sender.go
similarity index 87%
rename from server/mailer.go
rename to server/smtp_sender.go
index 22767212..15f004c1 100644
--- a/server/mailer.go
+++ b/server/smtp_sender.go
@@ -16,21 +16,21 @@ type mailer interface {
 	Send(from, to string, m *message) error
 }
 
-type smtpMailer struct {
+type smtpSender struct {
 	config *Config
 }
 
-func (s *smtpMailer) Send(senderIP, to string, m *message) error {
-	host, _, err := net.SplitHostPort(s.config.SMTPAddr)
+func (s *smtpSender) Send(senderIP, to string, m *message) error {
+	host, _, err := net.SplitHostPort(s.config.SMTPSenderAddr)
 	if err != nil {
 		return err
 	}
-	message, err := formatMail(s.config.BaseURL, senderIP, s.config.SMTPFrom, to, m)
+	message, err := formatMail(s.config.BaseURL, senderIP, s.config.SMTPSenderFrom, to, m)
 	if err != nil {
 		return err
 	}
-	auth := smtp.PlainAuth("", s.config.SMTPUser, s.config.SMTPPass, host)
-	return smtp.SendMail(s.config.SMTPAddr, auth, s.config.SMTPFrom, []string{to}, []byte(message))
+	auth := smtp.PlainAuth("", s.config.SMTPSenderUser, s.config.SMTPSenderPass, host)
+	return smtp.SendMail(s.config.SMTPSenderAddr, auth, s.config.SMTPSenderFrom, []string{to}, []byte(message))
 }
 
 func formatMail(baseURL, senderIP, from, to string, m *message) (string, error) {
diff --git a/server/mailer_test.go b/server/smtp_sender_test.go
similarity index 100%
rename from server/mailer_test.go
rename to server/smtp_sender_test.go
diff --git a/server/smtp_server.go b/server/smtp_server.go
new file mode 100644
index 00000000..f304dea8
--- /dev/null
+++ b/server/smtp_server.go
@@ -0,0 +1,108 @@
+package server
+
+import (
+	"bytes"
+	"errors"
+	"github.com/emersion/go-smtp"
+	"io"
+	"io/ioutil"
+	"log"
+	"net/mail"
+	"strings"
+	"sync"
+)
+
+// smtpBackend implements SMTP server methods.
+type smtpBackend struct {
+	config *Config
+	sub    subscriber
+}
+
+func newMailBackend(conf *Config, sub subscriber) *smtpBackend {
+	return &smtpBackend{
+		config: conf,
+		sub:    sub,
+	}
+}
+
+func (b *smtpBackend) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) {
+	return &smtpSession{config: b.config, sub: b.sub}, nil
+}
+
+func (b *smtpBackend) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) {
+	return &smtpSession{config: b.config, sub: b.sub}, nil
+}
+
+// smtpSession is returned after EHLO.
+type smtpSession struct {
+	config   *Config
+	sub      subscriber
+	from, to string
+	mu       sync.Mutex
+}
+
+func (s *smtpSession) AuthPlain(username, password string) error {
+	return nil
+}
+
+func (s *smtpSession) Mail(from string, opts smtp.MailOptions) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.from = from
+	return nil
+}
+
+func (s *smtpSession) Rcpt(to string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	addressList, err := mail.ParseAddressList(to)
+	if err != nil {
+		return err
+	} else if len(addressList) != 1 {
+		return errors.New("only one recipient supported")
+	} else if !strings.HasSuffix(addressList[0].Address, "@"+s.config.SMTPServerDomain) {
+		return errors.New("invalid domain")
+	} else if s.config.SMTPServerAddrPrefix != "" && !strings.HasPrefix(addressList[0].Address, s.config.SMTPServerAddrPrefix) {
+		return errors.New("invalid address")
+	}
+	// FIXME check topic format
+	s.to = addressList[0].Address
+	return nil
+}
+
+func (s *smtpSession) Data(r io.Reader) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	b, err := ioutil.ReadAll(r)
+	if err != nil {
+		return err
+	}
+
+	log.Println("Data:", string(b))
+	msg, err := mail.ReadMessage(bytes.NewReader(b))
+	if err != nil {
+		return err
+	}
+	body, err := io.ReadAll(msg.Body)
+	if err != nil {
+		return err
+	}
+	topic := strings.TrimSuffix(s.to, "@"+s.config.SMTPServerDomain)
+	m := newDefaultMessage(topic, string(body))
+	subject := msg.Header.Get("Subject")
+	if subject != "" {
+		m.Title = subject
+	}
+	return s.sub(m)
+}
+
+func (s *smtpSession) Reset() {
+	s.mu.Lock()
+	s.from = ""
+	s.to = ""
+	s.mu.Unlock()
+}
+
+func (s *smtpSession) Logout() error {
+	return nil
+}