TidyCal error 550 5.7.708 automatic calendar invites trigger ‘suspicious IP address’ warning

Question

I have connected a TidyCal account to my Microsoft business account. TidyCal creates a Teams meeting and sends out calendar invitations automatically, but I keep receiving an error email from Microsoft stating that the IP address is suspicious. The email is sent from a business account that is not the admin account. Both TidyCal and my hosting provider say that I should contact Microsoft about this but I cannot figure out how to fix this. The link I receive (see below) does not lead to the problem to my answer. This is the response I get after trying to send out an automatic email through TidyCal:

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(7230) [Moderator note: personal info removed] 2026-02-26T15:27:32.415Z [Moderator note: personal info removed]]'

Does anyone know how to fix this, please?

Answer 1

Yes, I am now in contact with the Microsoft helpdesk through my admin account. It is still not fixed but I am getting help. Thank you very much.

Answer 2

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hi @Tara

Thank you for posting your question in the Microsoft Q&A forum. 

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.

As the Q&A Assist already mentioned, to resolve the issue, you’ll need to open a support ticket in the Microsoft 365 Admin Center and request an IP address exception for your tenant.

To open a support ticket, log in https://admin.microsoft.com/ with your admin account. Then choose Help & Support, briefly describe your situation and provide details like error message.

I hope this information is helpful. 

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Answer 3

The error 550 5.7.708 Access denied, traffic not accepted from this IP means Microsoft 365 is rejecting mail because the sending IP address (used by TidyCal) currently has a low or suspicious reputation.

Key points from the error and behavior:

• The message is being sent through Microsoft 365 on behalf of the TidyCal integration.
• Microsoft 365 is blocking the traffic based on the source IP reputation, not on the content of the message.
• This is common for new or third‑party services that send via Microsoft 365 or for trial/low‑volume tenants.

Resolution steps:

1. Only an email admin in the Microsoft 365 tenant can fix this. The admin must handle the request; a normal user account cannot clear this on its own.
2. The admin should review the guidance for NDR 5.7.708 and then contact Microsoft Support to request an exception for the affected IP address. For trial or newer tenants, Microsoft explicitly recommends requesting an IP exception until licenses are fully assigned.
3. After Microsoft Support confirms the IP has been allowed or the restriction removed, new TidyCal‑generated Teams invitations should start sending successfully.

Because the block is on Microsoft’s side and tied to IP reputation, TidyCal and the hosting provider cannot resolve it themselves; it must be handled by the Microsoft 365 tenant admin working with Microsoft Support.

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References:

• NDR error codes 550 5.7.703, 550 5.7.705, 550 5.7.708, and 550 5.7.750