其背后的主要原因是环境变量的配置错误.更新您的config/mail.php文件.将变量值从env('varname', 'value')替换为'value'.

The main reason behind this is wrong configuration of environment variables. Update your config/mail.php file. Replace the variable values from env('varname', 'value') to 'value'.

这是一个例子(为我工作！):

Here's an example (Worked For Me!):

<?php

return [

    /*
    |--------------------------------------------------------------------------
    | Mail Driver
    |--------------------------------------------------------------------------
    |
        | Laravel supports both SMTP and PHP's "mail" function as drivers for the
    | sending of e-mail. You may specify which one you're using throughout
    | your application here. By default, Laravel is setup for SMTP mail.
    |
    | Supported: "smtp", "mail", "sendmail", "mailgun", "mandrill", "ses", "log"
    |
    */

    'driver' => 'mailgun',

    /*
    |--------------------------------------------------------------------------
    | SMTP Host Address
    |--------------------------------------------------------------------------
    |
    | Here you may provide the host address of the SMTP server used by your
    | applications. A default option is provided that is compatible with
    | the Mailgun mail service which will provide reliable deliveries.
    |
    */

    'host' => 'smtp.mailgun.org',

    /*
    |--------------------------------------------------------------------------
    | SMTP Host Port
    |--------------------------------------------------------------------------
    |
    | This is the SMTP port used by your application to deliver e-mails to
    | users of the application. Like the host we have set this value to
    | stay compatible with the Mailgun e-mail application by default.
    |
    */

    'port' => 587,

    /*
    |--------------------------------------------------------------------------
    | Global "From" Address
    |--------------------------------------------------------------------------
    |
    | You may wish for all e-mails sent by your application to be sent from
    | the same address. Here, you may specify a name and address that is
    | used globally for all e-mails that are sent by your application.
    |
    */

    'from' => ['address' => 'mail@yourdomain.com', 'name' => 'AppName'],

    /*
    |--------------------------------------------------------------------------
    | E-Mail Encryption Protocol
    |--------------------------------------------------------------------------
    |
    | Here you may specify the encryption protocol that should be used when
    | the application send e-mail messages. A sensible default using the
    | transport layer security protocol should provide great security.
    |
    */

    'encryption' => 'tls',

    /*
    |--------------------------------------------------------------------------
    | SMTP Server Username
    |--------------------------------------------------------------------------
    |
    | If your SMTP server requires a username for authentication, you should
    | set it here. This will get used to authenticate with your server on
    | connection. You may also set the "password" value below this one.
    |
    */

    'username' => null,

    /*
    |--------------------------------------------------------------------------
    | SMTP Server Password
    |--------------------------------------------------------------------------
    |
    | Here you may set the password required by your SMTP server to send out
    | messages from your application. This will be given to the server on
    | connection so that the application will be able to send messages.
    |
    */

    'password' => null,

    /*
    |--------------------------------------------------------------------------
    | Sendmail System Path
    |--------------------------------------------------------------------------
    |
    | When using the "sendmail" driver to send e-mails, we will need to know
    | the path to where Sendmail lives on this server. A default path has
    | been provided here, which will work well on most of your systems.
    |
    */

    'sendmail' => '/usr/sbin/sendmail -bs',

    /*
    |--------------------------------------------------------------------------
    | Mail "Pretend"
    |--------------------------------------------------------------------------
    |
    | When this option is enabled, e-mail will not actually be sent over the
    | web and will instead be written to your application's logs files so
    | you may inspect the message. This is great for local development.
    |
    */

    'pretend' => false,
];