bulk sender

[arab-mo80]

When I say send to clients from bulk sender program

Using smtp office365

Delivery has failed to these recipients or groups:

gps.gav@gmail.com
Your message wasn't delivered because the recipient's email provider rejected it.

Diagnostic information for administrators:

Generating server: MN2PR11MB4351.namprd11.prod.outlook.com

gps.gav@ntlworld.com
Remote Server returned '550 5.7.705 Service unavailable. Access denied, tenant has exceeded threshold. For more information please go to http://go.microsoft.com/fwlink/?LinkId=526653 S(7136) [MN2PR11MB3901.namprd11.prod.outlook.com]'

Original message headers:

Received: from MN2PR11MB4351.namprd11.prod.outlook.com
 ([fe80::3432:4ca0:4e0b:9aba]) by MN2PR11MB4351.namprd11.prod.outlook.com
 ([fe80::3432:4ca0:4e0b:9aba%4]) with mapi id 15.20.2644.015; Thu, 16 Jan 2020
 23:06:17 +0000
MIME-Version: 1.0
Content-Type: text/plain
Date: Thu, 16 Jan 2020 23:06:17 +0000
Message-ID: <212022537460010131287@admin-PC>
Subject: tech shop

[#2]

Using Office 365 to send bulk messages is a bad idea, and will result in the exact behavior you are observing - your user(s) or even tenant being blocked from sending messages. Use a service that specializes in bulk sending instead, or spin up a mail server.