Symfony 1.4 sfMailer：配置TLS自签名证书-无法找到套接字传输“ starttls”

Question

使用Swiftmailer 4.1.3的Symfony 1.4项目从4.1.0-dev升级

mailer:
    class: sfMailer
    param:
      delivery_strategy:  realtime
      delivery_address:   user@mail.com
      transport:
        class: Swift_SmtpTransport
        param:
          host:       x.x.x.x
          port:       25
          encryption: ~
          username:   user@mail.com
          password:   pass
          streamOptions:
            ssl:
                allow_self_signed: true
                verify_peer: false
                local_cert: "/etc/ssl/certificate.cer"
                local_pk: "/etc/ssl/certificate.key"

收到此错误：

Connection could not be established with host [Unable to find the socket transport "starttls" - did you forget to enable it when you configured PHP? #835125409]

如果我将加密更改为TLS，则会收到相同的错误。

Openssl已启用且正在运行。

有什么问题的主意吗？ PHP版本是5.4