diff --git a/services/mailer/token/token.go b/services/mailer/token/token.go
index 8a5a762d6b..1a52bce803 100644
--- a/services/mailer/token/token.go
+++ b/services/mailer/token/token.go
@@ -22,9 +22,16 @@ import (
 //
 // The payload is verifiable by the generated HMAC using the user secret. It contains:
 // | Timestamp | Action/Handler Type | Action/Handler Data |
+//
+//
+// Version changelog
+//
+// v1 -> v2:
+// Use 128 instead of 80 bits of the HMAC-SHA256 output.
 
 const (
 	tokenVersion1        byte = 1
+	tokenVersion2        byte = 2
 	tokenLifetimeInYears int  = 1
 )
 
@@ -70,7 +77,7 @@ func CreateToken(ht HandlerType, user *user_model.User, data []byte) (string, er
 		return "", err
 	}
 
-	return encodingWithoutPadding.EncodeToString(append([]byte{tokenVersion1}, packagedData...)), nil
+	return encodingWithoutPadding.EncodeToString(append([]byte{tokenVersion2}, packagedData...)), nil
 }
 
 // ExtractToken extracts the action/user tuple from the token and verifies the content
@@ -84,7 +91,7 @@ func ExtractToken(ctx context.Context, token string) (HandlerType, *user_model.U
 		return UnknownHandlerType, nil, nil, &ErrToken{"no data"}
 	}
 
-	if data[0] != tokenVersion1 {
+	if data[0] != tokenVersion2 {
 		return UnknownHandlerType, nil, nil, &ErrToken{fmt.Sprintf("unsupported token version: %v", data[0])}
 	}
 
@@ -124,5 +131,8 @@ func generateHmac(secret, payload []byte) []byte {
 	mac.Write(payload)
 	hmac := mac.Sum(nil)
 
-	return hmac[:10] // RFC2104 recommends not using less then 80 bits
+	// RFC2104 section 5 recommends that if you do HMAC truncation, you should use
+	// the max(80, hash_len/2) of the leftmost bits.
+	// For SHA256 this works out to using 128 of the leftmost bits.
+	return hmac[:16]
 }
diff --git a/tests/integration/incoming_email_test.go b/tests/integration/incoming_email_test.go
index fdc0425b54..66f833b28d 100644
--- a/tests/integration/incoming_email_test.go
+++ b/tests/integration/incoming_email_test.go
@@ -4,6 +4,7 @@
 package integration
 
 import (
+	"encoding/base32"
 	"io"
 	"net"
 	"net/smtp"
@@ -75,6 +76,51 @@ func TestIncomingEmail(t *testing.T) {
 		assert.Equal(t, payload, p)
 	})
 
+	tokenEncoding := base32.StdEncoding.WithPadding(base32.NoPadding)
+	t.Run("Deprecated token version", func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
+
+		payload := []byte{1, 2, 3, 4, 5}
+
+		token, err := token_service.CreateToken(token_service.ReplyHandlerType, user, payload)
+		require.NoError(t, err)
+		assert.NotEmpty(t, token)
+
+		// Set the token to version 1.
+		unencodedToken, err := tokenEncoding.DecodeString(token)
+		require.NoError(t, err)
+		unencodedToken[0] = 1
+		token = tokenEncoding.EncodeToString(unencodedToken)
+
+		ht, u, p, err := token_service.ExtractToken(db.DefaultContext, token)
+		require.ErrorContains(t, err, "unsupported token version: 1")
+		assert.Equal(t, token_service.UnknownHandlerType, ht)
+		assert.Nil(t, u)
+		assert.Nil(t, p)
+	})
+
+	t.Run("MAC check", func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
+
+		payload := []byte{1, 2, 3, 4, 5}
+
+		token, err := token_service.CreateToken(token_service.ReplyHandlerType, user, payload)
+		require.NoError(t, err)
+		assert.NotEmpty(t, token)
+
+		// Modify the MAC.
+		unencodedToken, err := tokenEncoding.DecodeString(token)
+		require.NoError(t, err)
+		unencodedToken[len(unencodedToken)-1] ^= 0x01
+		token = tokenEncoding.EncodeToString(unencodedToken)
+
+		ht, u, p, err := token_service.ExtractToken(db.DefaultContext, token)
+		require.ErrorContains(t, err, "verification failed")
+		assert.Equal(t, token_service.UnknownHandlerType, ht)
+		assert.Nil(t, u)
+		assert.Nil(t, p)
+	})
+
 	t.Run("Handler", func(t *testing.T) {
 		t.Run("Reply", func(t *testing.T) {
 			checkReply := func(t *testing.T, payload []byte, issue *issues_model.Issue, commentType issues_model.CommentType) {