Whitelist IP as safe sender
We have one appliance hosted on an external IP address. The appliance has SMTP configuration. When we give SMTP configs for O365, delivery to external recipients fails but internal recipients are able to receive the message successfully.
Tried adding IP to allow list in Connection filter in Defender portal but still unable to send emails to external users.
Error: Failed to send an email from the user with id '11' to the user with id '-99' due to the following error: "SMTP Error: The following recipients failed: : TenantAttribution; Relay Access Denied [TO1CAN01FT012.eop-CAN01.prod.protection.outlook.com] "