Sudden Exchange calendar disconnection – IONOS hosted Exchange / EWS – Anyone else experiencing this?

Hi everyone,

I'm reaching out to see if anyone else has experienced a similar issue with Calendly's Exchange calendar integration.

On October 24, at approximately 4:10 PM (French time), I received an email from Calendly notifying me that my Exchange calendar had been disconnected.

Until that moment, everything had been working perfectly for a long time. I had not changed my password, account settings, or server configuration.

My setup:

• Microsoft Exchange 2019 hosted by IONOS (not Microsoft 365 / Exchange Online)

• EWS server: https://exchange2019.ionos.eu/EWS/Exchange.asmx

• Outlook for Mac

• One Calendly account with several event types, including events managed by a partner organization for which I work as a subcontracted coach

What I've checked so far:

• My Exchange account works perfectly in Outlook.

• Outlook Web App (OWA) is accessible.

• My credentials are correct.

• Multiple attempts to reconnect Exchange to Calendly have failed.

• Most importantly, I successfully connected the exact same Exchange account to Cal.com and tested calendar synchronization. It works, including the creation of appointments in my Outlook calendar.

This last point is particularly interesting because it suggests that the issue may be specific to Calendly's Exchange integration, rather than my Exchange account itself.

Why this is a serious issue for me:

My Calendly account is also used by an organization I subcontract for. They manage several of my booking event types directly through Calendly, so switching to another scheduling platform is not a realistic workaround.

The disconnection is therefore affecting both my own business and my subcontracted coaching appointments.

I have already contacted Calendly support, but the issue remains unresolved.

My questions to the community:

1. Has anyone else experienced a sudden disconnection ?

2. Is anyone currently experiencing problems reconnecting an Exchange calendar through EWS?

3. Could this be related to a recent change in Calendly's Exchange authentication or integration?

I would really appreciate hearing from anyone experiencing similar issues, or from the Calendly technical team if they have any insight into what may have changed.

I'm particularly interested in understanding why a previously working integration suddenly stopped functioning, while the same Exchange account continues to work with another scheduling platform.

Thank you in advance for your help!