Why is html code displayed when sending an email in Laravel?

Question

Laravel

Good afternoon.
Deployed basic registration in Laravel 6 application.
Enabled email confirmation, again in a standard way
Sending a letter via smtp google
The problem is that the letter arrives, but its layout is displayed.

<tr>
    <td align="center">
        <table width="100%" border="0" cellpadding="0" cellspacing="0" role="presentation">
            <tr>
                <td align="center">
                    <table border="0" cellpadding="0" cellspacing="0" role="presentation">
                        <tr>
                            <td>
                                <a href="http://127.0.0.1:8000/email/verify/2/e80bb47e7cf60250f5af1306cd2f9a5b1a28b7ca?expires=1578076001&amp;signature=047f46c7caf69e5b538a99f123b4033b05d49e6f876915dd2fd0dedb436d0c94" class="button button-primary" target="_blank">Verify Email Address</a>
                            </td>
                        </tr>
                    </table>
                </td>
            </tr>
        </table>
    </td>
</tr>

I looked at the message headers and saw
MIME-Version: 1.0
Content-Type: multipart/alternative;
Before this, there was no such problem.
Why could this happen and how can it be fixed?