Dear All!
We are using exhange online and some external domain is trying to send us a mail, and it gets refused with the following NDR:
ourdomain.mail.protection.outlook.com[104.47.x.x] said: 550 5.7.1
Service unavailable, Client host [193.169.x.x] blocked using Customer
Block list AS(1420) [DB5EUR03FT004.eop-EUR03.prod.protection.outlook.com]
(in reply to RCPT TO command)
The sent email in our tracking log do not appear. It is not in quarantine. Why should...we send back an ndr, but i am out of ideas... In EXO security center checked the antispam and phishing settings but i did not found relevant settings.
How sould I resolve this problem, what should i check?
Do you need any more information about the case?
Thanks
Peter
