<?php
$htmlContent = "<strong>Welcome</strong> <br/> <h1>FieldBlaze</h1>";

 $mailgun = [
     'apiKey' => '2f5d2dac443367a7a0341afaf1449d99-2fbe671d-39be13b6',
     'domain' => 'fieldblaze.com',
 ];

 $ch = curl_init();

 curl_setopt( $ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC );
 curl_setopt( $ch, CURLOPT_USERPWD, "api:{$mailgun['apiKey']}" );
 curl_setopt( $ch, CURLOPT_RETURNTRANSFER, 1 );

 curl_setopt( $ch, CURLOPT_CUSTOMREQUEST, 'POST' );
 curl_setopt( $ch, CURLOPT_URL, "https://api.mailgun.net/v3/{$mailgun['domain']}/messages" );
 curl_setopt( $ch, CURLOPT_POSTFIELDS,
     [
         'from' => "FieldBlaze <sales@{$mailgun['domain']}>",
         'to' => 'rohit@cccinfotech.com',
         'to' => 'naeem@cccinfotech.com',
         'subject' => 'Scheduled Demo - FieldBlaze',
         'text' => "This ".time()." is a new line\nThe next line.\r\nLine after CRLF.\n<strong>This won't work unless you use the 'html' param.</strong>",
         'html'    => $htmlContent,
     ]
 );

 $result = curl_exec( $ch );
 curl_close( $ch );

 print_r( $result );
 /*
 Success response is like:
     {
         "id": "20210611034145.1.3C55988607CF320B@example.com",
         "message": "Queued. Thank you."
     }
 */