Your configuration does not allow connections to http://packagist.phpcomposer.com/packages.json. See https://getcomposer.org/doc/06-config.md#secure-http for details.
初次看来可能是配置文件的原因
输入
composer config secure-http false意义是默认禁用https请求
再输入
composer search phpmailer
来安装
composer require phpmailer/phpmailer
