diff --git a/go.mod b/go.mod
index c51f0df..d65fd4a 100644
--- a/go.mod
+++ b/go.mod
@@ -9,7 +9,7 @@ require (
 	github.com/emersion/go-imap v1.2.1
 	github.com/emersion/go-mbox v1.0.3
 	github.com/emersion/go-message v0.17.0
-	github.com/emersion/go-smtp v0.19.0
+	github.com/emersion/go-smtp v0.21.1
 	github.com/emersion/go-vcard v0.0.0-20230815062825-8fda7d206ec9
 	github.com/emersion/go-webdav v0.3.2-0.20220524091811-5d845721d8f7
 	golang.org/x/crypto v0.15.0
diff --git a/go.sum b/go.sum
index a763765..c6363af 100644
--- a/go.sum
+++ b/go.sum
@@ -19,8 +19,8 @@ github.com/emersion/go-message v0.17.0/go.mod h1:/9Bazlb1jwUNB0npYYBsdJ2EMOiiyN3
 github.com/emersion/go-sasl v0.0.0-20200509203442-7bfe0ed36a21/go.mod h1:iL2twTeMvZnrg54ZoPDNfJaJaqy0xIQFuBdrLsmspwQ=
 github.com/emersion/go-sasl v0.0.0-20231106173351-e73c9f7bad43 h1:hH4PQfOndHDlpzYfLAAfl63E8Le6F2+EL/cdhlkyRJY=
 github.com/emersion/go-sasl v0.0.0-20231106173351-e73c9f7bad43/go.mod h1:iL2twTeMvZnrg54ZoPDNfJaJaqy0xIQFuBdrLsmspwQ=
-github.com/emersion/go-smtp v0.19.0 h1:iVCDtR2/JY3RpKoaZ7u6I/sb52S3EzfNHO1fAWVHgng=
-github.com/emersion/go-smtp v0.19.0/go.mod h1:qm27SGYgoIPRot6ubfQ/GpiPy/g3PaZAVRxiO/sDUgQ=
+github.com/emersion/go-smtp v0.21.1 h1:VQeZSZAKk8ueYii1yR5Zalmy7jI287eWDUqSaJ68vRM=
+github.com/emersion/go-smtp v0.21.1/go.mod h1:qm27SGYgoIPRot6ubfQ/GpiPy/g3PaZAVRxiO/sDUgQ=
 github.com/emersion/go-textwrapper v0.0.0-20200911093747-65d896831594 h1:IbFBtwoTQyw0fIM5xv1HF+Y+3ZijDR839WMulgxCcUY=
 github.com/emersion/go-textwrapper v0.0.0-20200911093747-65d896831594/go.mod h1:aqO8z8wPrjkscevZJFVE1wXJrLpC5LtJG7fqLOsPb2U=
 github.com/emersion/go-vcard v0.0.0-20191221110513-5f81fa0d3cc7/go.mod h1:HMJKR5wlh/ziNp+sHEDV2ltblO4JD2+IdDOWtGcQBTM=
diff --git a/smtp/smtp.go b/smtp/smtp.go
index 6df1006..31ecb99 100644
--- a/smtp/smtp.go
+++ b/smtp/smtp.go
@@ -11,6 +11,7 @@ import (
 	"github.com/ProtonMail/go-crypto/openpgp"
 	"github.com/ProtonMail/go-crypto/openpgp/packet"
 	"github.com/emersion/go-message/mail"
+	"github.com/emersion/go-sasl"
 	"github.com/emersion/go-smtp"
 
 	"github.com/emersion/hydroxide/auth"
@@ -377,7 +378,16 @@ type session struct {
 	allReceivers []string
 }
 
-func (s *session) AuthPlain(username, password string) error {
+var _ interface {
+	smtp.Session
+	smtp.AuthSession
+} = (*session)(nil)
+
+func (s *session) AuthMechanisms() []string {
+	return []string{sasl.Plain}
+}
+
+func (s *session) authPlain(username, password string) error {
 	c, privateKeys, err := s.be.sessions.Auth(username, password)
 	if err != nil {
 		return err
@@ -403,6 +413,15 @@ func (s *session) AuthPlain(username, password string) error {
 	return nil
 }
 
+func (s *session) Auth(mech string) (sasl.Server, error) {
+	return sasl.NewPlainServer(func(identity, username, password string) error {
+		if identity != "" && identity != username {
+			return fmt.Errorf("invalid SASL PLAIN identity")
+		}
+		return s.authPlain(username, password)
+	}), nil
+}
+
 func (s *session) Mail(from string, options *smtp.MailOptions) error {
 	if s.c == nil {
 		return smtp.ErrAuthRequired