发送邮件出错 For testing purposes

在使用双翼邮件群发软件发送邮件出现下面错误
Error: 421 Error: For testing purposes you can only send emails to yourmail@gmail.com that was used to register your Elastic Email account. Please purchase one of our plan options to send emails to your intended recipients.
出现这个错误的原因是你正在使用的发送邮箱是免费邮箱，只能发给指定的邮箱（也就是你自己的邮箱），付费后才能正常发送其他邮箱。