Created dev O365 Tenant to test email, everyting blocked with "5.7.708 Service unavailable"

Copper Contributor

A couple of days ago, I created a development O365 tenant with my Visual Studio subscription, in order to try to implement Exchange-Online-based email notifications in my software. Everything seems to be working (I'm using the Graph API to send emails), but I always get a message in the sender's inbox similar to this:


Diagnostic information for administrators:

Generating server:

Remote server returned '550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP. For more information please go to AS(7230) [ 2023...


I just got this tenant, and I've never managed to send a single email successfully. Are the dev tenants just on all the block lists because people were using them to spam?


Anyone have any suggestions?

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