Outbound external email is rejected with 550 5.7.708 ‘Service unavailable.

Hi Anthony Wotring

You’re seeing the 550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP error because Microsoft’s outbound mail protection is blocking traffic from your tenant or the IP address used by the integration.

If you’re on a trial subscription, this is expected behavior until licenses are assigned. In this case, I would recommend moving to a paid Microsoft 365 / Exchange Online subscription rather than relying on the trial tenant for production email sending.

After the paid licenses have been purchased and assigned, if outbound mail is still being blocked, the tenant administrator can then contact Microsoft Support and request an IP address exception for your tenant as mentioned in NDR error codes 550 5.7.703, 550 5.7.705, 550 5.7.708, and 550 5.7.750 - Microsoft Support(Only Microsoft Support can grant an IP exception, this cannot be resolved by tenant-side configuration alone).

For instructions on raising a support ticket, please refer to: Get support - Microsoft 365 admin | Microsoft Learn.

I hope this information is helpful and if you have any further question, please feel free to ask via comment section.

(Please understand that we're not Microsoft support, this is a user-to-user support forum. Moderators have no backend access and cannot directly intervene in Microsoft products. We provide only technical guidance and best-practice recommendations based on reported issues) 

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