test email fail // exceeded number of messages

I’ve sent a test email and got the error below. Now from the wording it would suggest that the system is sending too many emails to one email address but the test email address is completely new so that can’t be the issue. The other issue I thought is that the system has sent too many emails for Outlook’s liking but the system shouldn’t have sent any emails since Tuesday so not sure why the error would still be coming up.

SMTP protocol isn’t really my area hence we’re using the plugin, any insight into what I’m missing here I would be very grateful for. Thank you.

Versions:
WordPress: 4.9.6
WordPress MS: No
PHP: 5.6.36-1+ubuntu16.04.1+deb.sury.org+1
WP Mail SMTP: 1.2.5

Params:
Mailer: smtp
Constants: Yes
ErrorInfo: SMTP Error: data not accepted.SMTP server error: DATA END command failed Detail: 5.2.125 The sender has exceeded the maximum number of messages they are allowed to send via client submission either per minute or per day. [DB6PR0501MB2295.eurprd05.prod.outlook.com]
SMTP code: 550
Host: smtp.office365.com
Port: 587
SMTPSecure: tls