Add SMTP_HELLO_NAME to let operators set the EHLO/HELO identity

Google Workspace SMTP relay (smtp-relay.gmail.com) rejects generic
EHLO identifiers such as "localhost", which is Go net/smtp's default.
Operators can now set SMTP_HELLO_NAME to a valid hostname so that
c.Hello() is called before StartTLS, satisfying strict relay policies.

Fixes https://github.com/getprobo/probo/issues/1284

Signed-off-by: Bryan Frimin <bryan@probo.com>

pkg/bootstrap/builder.go

@@ -166,6 +166,7 @@ func (b *Builder) Build() (*probodconfig.FullConfig, error) {
 						User:        b.getEnv("SMTP_USER"),
 						Password:    b.getEnv("SMTP_PASSWORD"),
 						TLSRequired: b.getEnvBoolOrDefault("SMTP_TLS_REQUIRED", false),
+						HelloName:   b.getEnv("SMTP_HELLO_NAME"),
 					},
 				},
 				Slack: probodconfig.SlackConfig{

pkg/bootstrap/builder_test.go

@@ -192,6 +192,7 @@ func TestBuilder_Build_Defaults(t *testing.T) {
 	assert.Equal(t, "no-reply@notification.getprobo.com", cfg.Probod.Notifications.Mailer.SenderEmail)
 	assert.Equal(t, "localhost:1025", cfg.Probod.Notifications.Mailer.SMTP.Addr)
 	assert.False(t, cfg.Probod.Notifications.Mailer.SMTP.TLSRequired)
+	assert.Empty(t, cfg.Probod.Notifications.Mailer.SMTP.HelloName)
 	assert.Equal(t, 60, cfg.Probod.Notifications.Mailer.MailerInterval)
 	assert.Equal(t, 60, cfg.Probod.Notifications.Slack.SenderInterval)
 	assert.Empty(t, cfg.Probod.Notifications.Slack.SigningSecret)

pkg/mailer/mailer.go

@@ -49,6 +49,7 @@ type (
 		User        string
 		Password    string
 		TLSRequired bool
+		HelloName   string
 	}
 
 	SendingWorkerOption func(*sendingHandler)
@@ -319,6 +320,12 @@ func (h *sendingHandler) sendMail(ctx context.Context, to []string, msg []byte)
 
 	defer func() { _ = c.Quit() }()
 
+	if h.smtp.HelloName != "" {
+		if err := c.Hello(h.smtp.HelloName); err != nil {
+			return fmt.Errorf("SMTP EHLO error: %w", err)
+		}
+	}
+
 	if h.smtp.TLSRequired {
 		if err := c.StartTLS(&tls.Config{ServerName: host}); err != nil {
 			return fmt.Errorf("TLS negotiation error: %w", err)

pkg/probod/probod.go

@@ -654,6 +654,7 @@ func (impl *Implm) Run(
 			User:        impl.cfg.Notifications.Mailer.SMTP.User,
 			Password:    impl.cfg.Notifications.Mailer.SMTP.Password,
 			TLSRequired: impl.cfg.Notifications.Mailer.SMTP.TLSRequired,
+			HelloName:   impl.cfg.Notifications.Mailer.SMTP.HelloName,
 		},
 		l.Named("sending-worker"),
 		[]mailer.SendingWorkerOption{

pkg/probodconfig/mailer_config.go

@@ -26,4 +26,5 @@ type SMTPConfig struct {
 	User        string `json:"user"`
 	Password    string `json:"password"`
 	TLSRequired bool   `json:"tls-required"`
+	HelloName   string `json:"hello-name"`
 }