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How to Fix Calendly Invitation Error 550 5.7.708 in Microsoft 365
Question details
The user needs to resolve an issue where automated Calendly invitations sent through Microsoft 365 fail to deliver due to an IP block.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Sending automated calendar invitations using Calendly integrated with Microsoft 365.
- Observed behavior
- Regular emails send successfully, but automated Calendly invites fail with the bounce back error '550 5.7.708 Service unavailable; access denied; traffic not accepted from this IP'.
Ensure you have Microsoft 365 global administrator permissions, as resolving IP blocklist issues requires access to the Exchange admin center and Microsoft's security portals.
Submit a Support Request via the Microsoft 365 Admin Center
The most effective way to resolve tenant-level IP blocks (NDR errors 5.7.700 through 5.7.750) is by having an administrator contact Microsoft Support directly.
Because Calendly's automated email service routes messages through a different sending path than your standard Outlook emails, Microsoft 365 may flag and block the specific IP address used by Calendly due to reputation checks.
Navigate to the Microsoft 365 Admin Center at https://admin.microsoft.com and log in with your administrator credentials.
Locate the 'Support' section on the left-hand navigation menu and click on 'New service request' or 'Help & support'.
Describe the issue clearly, mentioning the specific NDR error code '550 5.7.708' and explaining that legitimate Calendly invitation traffic is being blocked.
Submit the support ticket and wait for a Microsoft support engineer to review and unblock the affected IP address or tenant.
Check the Restricted Entities Portal
Verify if the sending user or IP has been automatically restricted by Microsoft's anti-spam filters.
Use the Microsoft Anti-Spam IP Delist Portal
Manually request Microsoft to remove a specific IP address from their blocked sender list.
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Frequently Asked Questions
Why does my regular Microsoft 365 email work but Calendly invites fail with error 5.7.708?
Calendly's automated email service routes messages through a different sending path and IP address than your regular Outlook emails. If Microsoft 365 detects suspicious traffic from that specific IP, it blocks it, while your normal emails remain unaffected.
How long does it take to unblock an IP address in Microsoft 365?
Once an IP address is removed from the blocklist via the delist portal or a Microsoft support ticket, it can take up to 24 hours for the reputation changes to propagate across Microsoft's global servers.
Can a regular user fix the 550 5.7.708 error?
No, resolving this specific NDR error requires administrative privileges. You must contact your organization's Microsoft 365 IT administrator to access the admin center, review restricted users, or submit a service request to Microsoft.
How do I find the blocked IP address to submit to the delist portal?
Open the Non-Delivery Report (NDR) bounce email you received when the Calendly invite failed. The specific blocked IP address will be clearly listed within the technical details section of the error message.
