最终解决了

$transport = Swift_smtpTransport::newInstance( "mx1.hostinger.co.uk" , 2525 );

事实上应该

$transport = Swift_SmtpTransport::newyInstance( "mx1.hostinger.co.uk" , 2525 );

然后我的托管服务提供商不允许我的计划通过 SMTP 发送邮件.

and then afterwards that my hosting provider does not allow mail to be sent by SMTP on my plan.