What you’re seeing
- Free/busy shows as blank, hatched or no information available for colleagues on the other platform.
- Cloud users can see each other's calendars but not those of on-premises users, or the reverse.
- Scheduling Assistant can't suggest meeting times across the two groups.
- Opening a shared calendar across platforms gives an error or never loads.
Common causes
Every environment is different, but these are the causes our engineers find most often:
- The OAuth trust between on-premises Exchange and Microsoft 365 is broken, often because the authorization certificate expired.
- Microsoft 365 cannot reach your on-premises Exchange web services or autodiscover from the internet.
- The organization relationship or intra-organization connector is missing domains or points to the wrong address.
- A reverse proxy in front of Exchange requires pre-authentication that free/busy requests from the cloud cannot pass.
- Mailbox users are missing the routing address that tells each side where the other mailbox lives.
Why it matters
Calendar visibility is what lets teams book meetings without long email chains. When free/busy breaks during a hybrid migration, people double-book, schedule over each other and miss meetings, and assistants who manage executives' calendars lose a core part of their job. The problem often appears gradually as more mailboxes move, which makes it feel like the migration is failing and erodes confidence in the project.
How AskTechGurus fixes it
Skip the trial and error. A certified engineer works on your actual system, finds the root cause, and fixes it properly.
Tell us what’s happening
Submit a ticket in about two minutes. Paste the error, describe what changed, and pick your tier. No charge to submit.
A certified engineer diagnoses it
A vetted, US-based systems engineer claims your ticket, usually within minutes during business hours, and investigates over a secure remote session you can watch and end at any time.
Fixed and verified with you
The engineer resolves the root cause and confirms with you that it’s working. You don’t just get a workaround, and you get a plain-English summary of what was wrong.
Pay only when it’s resolved
Fixed price from $99, invoiced only after you approve the fix. If it isn’t resolved, you don’t pay.
Frequently asked questions
Does this affect email delivery between the two sides?
Usually not. Calendar availability uses a different path from mail flow, so messages generally keep arriving normally even while free/busy is broken.
Will it fix itself as more mailboxes move to the cloud?
No. Users still split across the two environments will keep seeing the problem until the underlying trust or connectivity issue is resolved.