i am using office 365 email as a mail server, so the sending message limit is 30 per minute in office 365. when sending the mass mail like newsletters i got disconnected from server.  Is there any solution to reduce the sending speed or how can i overcome this issue. I getting following error.

Mail Delivery Failed Mail delivery failed via SMTP server 'None'. SMTPSenderRefused: 421 4.4.2 Message submission rate for this client has exceeded the configured limit [HE1PR10MB1674.EURPRD10.PROD.OUTLOOK.COM.