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When creating Calendar Events via the Graph API, the events are created correctly in the calendar of the organizer but the invites to the participants get bounced. The organizer gets a 'Delivery has failed...' message with the following error message:

Remote Server returned '550 5.7.708 Service unavailable. Access denied, traffic not accepted from this IP. For more information please go to http://go.microsoft.com/fwlink/?LinkId=526653 AS(7171)

Sending emails manually through Outlook (web) from the organizer to the participants works fine.

The issue is intermittent. After changing the DNS server, everything worked fine for some time.

I checked https://protection.office.com/restrictedusers as suggested in the answers to similar posts, but this list is empty.

I also tried delisting the IP address (my own?) through https://sender.office.com/, but to no avail.

The tenant is linked to the Microsoft Developer Program and would allegedly have a 'bad reputation'. However, I don't understand how that would explain the fact that it sometimes works and sometimes doesn't when sending exactly the same API request and hence 'triggering' exactly the same emails...

Jonas
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2 Answers2

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I think the best way to overcome this would be to add a domain to your developer tenant as per the guidance here:

https://learn.microsoft.com/en-us/Exchange/mail-flow-best-practices/non-delivery-reports-in-exchange-online/fix-error-code-5-7-700-through-5-7-750#57750-client-blocked-from-sending-from-unregistered-domain

Add and validate all domains in Office 365 that you use to send email messages. For more information, see Add a domain to Office 365.

I'm not guaranteeing this will resolve it. You have to understand that those developer tenants are only meant for experimentation and so there are checks and balances to ensure they are used in a bad manor.

How many emails are you sending through this tenant?

Jeremy Thake MSFT
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Calendar events are sent out via email. Add the "Mail.Send" permission to you App Registration.

This solved it for me.

Gazben
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