sender trying to send us 200 e-mail messages at once and we recived only about 20 e-mail messages.
Both sender and recipients are O365 but different organization(tenant)
Sender receive this error message:
Remote Server returned '550 5.1.8 Access denied, bad outbound sender AS(42003)' Original message headers: Received: from AM8PR05MB8274.eurprd05.prod.outlook.com
I'm admin for recipients tenant and if I do message trace only 20 e-mail messages are visible from this sender and 180 are not visible in message trace.
Any idea how to trubleshoot this?Bulk problem?
Is it sender or recipient tenant problem?
My default outbound policy is
And default inbound
I'm not sure what those number means