How resolve 'Remote server returned '550 5.7.708 Service unavailable.' error while send an email

[shivakarthik]

I am able to send mail through Graph API but it is not received by the recipient. I have added O365 licenses and given all the permissions to the application which was created in the Azure portal. An

access token is generated differently for the @outlook.com domain and onmicrosoft.com. Please help!screenshot from https://outlook.office.com/ 

[#2]

Hi @shivakarthik,

Based on the NDR you received, it seems that the IP address was tagged as a potential threat to Office 365 for some reasons.

Please use the Office 365 delist portal to remove yourself from the blocked senders list, that should solve your issue. You can see the instructions in this article: 

Remove yourself from the blocked senders list and address 5.7.511 Access denied errors | Microsoft L...

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Leon Pavesic