func runsslserver(t *testing.T, server *smtpd.Server) (addr string, closer func()) {
cert, err := tls.X509KeyPair(localhostCert, localhostKey)
if err != nil {
t.Fatalf("Cert load failed: %v", err)
}
server.TLSConfig = &tls.Config{
Certificates: []tls.Certificate{cert},
}
return runserver(t, server)
}