diff --git a/client_test.go b/client_test.go
index 8bad1e0..afc5743 100644
--- a/client_test.go
+++ b/client_test.go
@@ -9,6 +9,7 @@ import (
 	"crypto/tls"
 	"errors"
 	"fmt"
+	"io"
 	"net"
 	"os"
 	"strconv"
@@ -1269,3 +1270,114 @@ func getTestConnectionWithDSN(auth bool) (*Client, error) {
 	}
 	return c, nil
 }
+
+func TestXOAuth2OK(t *testing.T) {
+	server := []string{
+		"220 Fake server ready ESMTP",
+		"250-fake.server",
+		"250-AUTH LOGIN XOAUTH2",
+		"250 8BITMIME",
+		"250 OK",
+		"235 2.7.0 Accepted",
+		"250 OK",
+		"221 OK",
+	}
+	var wrote strings.Builder
+	var fake faker
+	fake.ReadWriter = struct {
+		io.Reader
+		io.Writer
+	}{
+		strings.NewReader(strings.Join(server, "\r\n")),
+		&wrote,
+	}
+	c, err := NewClient("fake.host",
+		WithDialContextFunc(getFakeDialFunc(fake)),
+		WithTLSPolicy(TLSOpportunistic),
+		WithSMTPAuth(SMTPAuthXOAUTH2),
+		WithUsername("user"),
+		WithPassword("token"))
+	if err != nil {
+		t.Fatalf("unable to create new client: %v", err)
+	}
+	if err := c.DialWithContext(context.Background()); err != nil {
+		t.Fatalf("unexpected dial error: %v", err)
+	}
+	if err := c.Close(); err != nil {
+		t.Fatalf("disconnect from test server failed: %v", err)
+	}
+	if !strings.Contains(wrote.String(), "AUTH XOAUTH2 dXNlcj11c2VyAWF1dGg9QmVhcmVyIHRva2VuAQE=\r\n") {
+		t.Fatalf("got %q; want AUTH XOAUTH2 dXNlcj11c2VyAWF1dGg9QmVhcmVyIHRva2VuAQE=\r\n", wrote.String())
+	}
+}
+
+func TestXOAuth2Unsupported(t *testing.T) {
+	server := []string{
+		"220 Fake server ready ESMTP",
+		"250-fake.server",
+		"250-AUTH LOGIN PLAIN",
+		"250 8BITMIME",
+		"250 OK",
+		"250 OK",
+		"221 OK",
+	}
+	var wrote strings.Builder
+	var fake faker
+	fake.ReadWriter = struct {
+		io.Reader
+		io.Writer
+	}{
+		strings.NewReader(strings.Join(server, "\r\n")),
+		&wrote,
+	}
+	c, err := NewClient("fake.host",
+		WithDialContextFunc(getFakeDialFunc(fake)),
+		WithTLSPolicy(TLSOpportunistic),
+		WithSMTPAuth(SMTPAuthXOAUTH2))
+	if err != nil {
+		t.Fatalf("unable to create new client: %v", err)
+	}
+	if err := c.DialWithContext(context.Background()); err == nil {
+		t.Fatal("expected dial error got nil")
+	} else {
+		if !errors.Is(err, ErrXOauth2AuthNotSupported) {
+			t.Fatalf("expected %v; got %v", ErrXOauth2AuthNotSupported, err)
+		}
+	}
+	if err := c.Close(); err != nil {
+		t.Fatalf("disconnect from test server failed: %v", err)
+	}
+	client := strings.Split(wrote.String(), "\r\n")
+	if len(client) != 5 {
+		t.Fatalf("unexpected number of client requests got %d; want 5", len(client))
+	}
+	if !strings.HasPrefix(client[0], "EHLO") {
+		t.Fatalf("expected EHLO, got %q", client[0])
+	}
+	if client[1] != "NOOP" {
+		t.Fatalf("expected NOOP, got %q", client[1])
+	}
+	if client[2] != "NOOP" {
+		t.Fatalf("expected NOOP, got %q", client[2])
+	}
+	if client[3] != "QUIT" {
+		t.Fatalf("expected QUIT, got %q", client[3])
+	}
+}
+
+func getFakeDialFunc(conn net.Conn) DialContextFunc {
+	return func(ctx context.Context, network, address string) (net.Conn, error) {
+		return conn, nil
+	}
+}
+
+type faker struct {
+	io.ReadWriter
+}
+
+func (f faker) Close() error                     { return nil }
+func (f faker) LocalAddr() net.Addr              { return nil }
+func (f faker) RemoteAddr() net.Addr             { return nil }
+func (f faker) SetDeadline(time.Time) error      { return nil }
+func (f faker) SetReadDeadline(time.Time) error  { return nil }
+func (f faker) SetWriteDeadline(time.Time) error { return nil }
diff --git a/smtp/smtp_test.go b/smtp/smtp_test.go
index e09cdf3..62d0f0b 100644
--- a/smtp/smtp_test.go
+++ b/smtp/smtp_test.go
@@ -200,7 +200,7 @@ func TestAuthLogin(t *testing.T) {
 	}
 }
 
-func TestXOAuthOK(t *testing.T) {
+func TestXOAuth2OK(t *testing.T) {
 	server := []string{
 		"220 Fake server ready ESMTP",
 		"250-fake.server",