You’re staring at a screen that won't budge. It’s frustrating. One minute you’re trying to sync your calendar or send an email through a third-party app, and the next, a blunt notification hits your screen: the request was denied by service delegate. It sounds like corporate jargon. It feels like a digital wall.
Most people think their password is wrong. It isn't. Others assume the server is down. Usually, that’s not it either.
This specific error is a handshake that failed. It’s an authentication breakdown between two services—usually involving Microsoft 365, Outlook, or Apple Mail—where one piece of software is trying to act on behalf of another. When the "delegate" (the app) asks for permission to do something, the "service" (the server) says no.
What’s Actually Happening Under the Hood?
Permissions are messy. In the world of enterprise software, "delegation" is the process where you give an app or another user the right to perform tasks for you. Think of it like a power of attorney for your inbox. When you see the request was denied by service delegate, the server is essentially saying, "I see you're trying to do this, but I don't trust the person or app you've sent to do it."
It happens a lot with macOS users trying to sync with Exchange. Apple Mail sends a request. Exchange looks at the request and realizes the token is expired or the account doesn't have "send-as" permissions. Instead of a helpful tip, you get the delegate error.
Sometimes it’s a global settings issue. If an IT admin changed a security policy over the weekend, your apps might still be trying to use the old "delegation" rules. The server rejects them instantly. It’s a security feature, honestly. It prevents unauthorized apps from scraping your data, but that’s cold comfort when you just need to send a PDF to your boss before a 9:00 AM meeting.
Common Triggers for the Request Was Denied by Service Delegate
Identity conflicts are usually the culprit. If you have a personal Microsoft account and a work account logged into the same device, the "delegate" might be getting confused about which identity it should present to the server.
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Keychain Corruption: On a Mac, the Keychain stores your "delegate" credentials. If that entry gets corrupted—which happens more than Apple likes to admit—the app sends "garbage" data to the server. The server sees the garbage and denies the request.
Expired OAuth Tokens: Modern apps don’t use your password every time. They use a "token." If that token expires and the app fails to refresh it automatically, the server views the next request as unauthorized.
Shared Mailbox Gremlins: This is a classic IT headache. You’re trying to send an email from a shared info@company.com address. You have access to the mailbox, but the "delegate" permissions aren't set to "Send As." You can read everything, but the moment you hit send, the service delegate denial kicks in.
Is it a Server Side or Client Side Issue?
Finding out who is at fault is half the battle.
Start by logging into the web version of your service. If you’re using Outlook, go to Outlook.com or your company's OWA. If you can send emails and manage your calendar there without a hitch, your account is fine. The problem is "client-side." Your app is the broken link.
If the web version also throws errors? That’s a "server-side" problem. You’ll need to talk to an admin because no amount of restarting your phone will fix a permission block on the server.
The Microsoft 365 and MacOS Conflict
There is a long-standing tension between how macOS handles EWS (Exchange Web Services) and how Microsoft prefers things to work. You'll often see the request was denied by service delegate right after an OS update. Apple tweaks how the mail client handles background syncing, and suddenly the "delegate" credentials aren't being passed correctly.
Microsoft’s move toward "Modern Authentication" (OAuth 2.0) changed the game. Older versions of Outlook or third-party mail apps that rely on "Basic Auth" are being systematically blocked. If your app is old, it’s not a bug; it’s a forced retirement.
How to Fix the Service Delegate Error Right Now
Don't just delete the app. That's overkill. Most of the time, you just need to clear the "identity" state.
Clear the Cached Credentials
On Windows, go to the Credential Manager. Look for anything labeled "MicrosoftOffice16" or "Outlook." Delete them. On a Mac, open Keychain Access and search for "Exchange" or "Office." Nuke those entries. When you restart the app, it will be forced to ask the server for a fresh, clean delegate token.
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Re-Add the Account (The Clean Way)
Sometimes the local database for your mail is just... done. It’s tired. If clearing credentials doesn't work, remove the account from your device entirely. Restart the device. Seriously, actually restart it. Then add the account back. This forces a complete re-negotiation of the delegate relationship between your device and the server.
Check Shared Permissions
If you are working in a team environment, have your admin check the "Delegate Access" settings in the Exchange Admin Center. There is a specific checkbox for "Recipient can see my private items" and "Send on Behalf." If these are toggled incorrectly, the service delegate will deny requests for certain types of actions while allowing others. It's incredibly granular.
Dealing with the "Send As" vs "Send on Behalf" Confusion
This is a nuance that trips up even seasoned sysadmins.
- Send As: The recipient sees the email coming exactly from the shared address.
- Send on Behalf: The recipient sees "Your Name on behalf of Shared Address."
If your app is configured to "Send As" but the server only gave you "Send on Behalf" rights, you guessed it: the request was denied by service delegate. The app is asking for a level of authority it doesn't have. Switching the settings to match your actual permissions usually clears the error instantly.
Why This Error is Becoming More Frequent
Security is getting tighter. Ten years ago, "delegation" was wide open. Today, with the rise of ransomware and phishing, services like Google Workspace and Microsoft 365 are much more skeptical. They want to see a clear, encrypted chain of custody for every request.
Every time a service updates its API—the language apps use to talk to each other—there is a risk that the "delegate" logic will break. We are seeing a massive shift toward "Least Privilege" architecture. This means if an app doesn't explicitly need a permission, it doesn't get it. If you try to use a feature that falls outside that tiny circle of permission, the service delegate shuts you down.
It's also worth noting that VPNs and firewalls play a role. If your VPN is masking your IP in a way that makes the server think you’re in a different country, it might revoke your delegate status as a protective measure. The server thinks, "Wait, why is a delegate from a known suspicious IP trying to access this calendar?" Denial is the default response.
Steps for IT Administrators
If you’re the one who has to fix this for a whole office, check the Azure AD (Entra ID) sign-in logs. Look for "Failure" statuses. The logs will often give you a specific error code like 50196 or 50076. These codes tell you exactly why the delegate was rejected—whether it’s a Multi-Factor Authentication (MFA) requirement or a Conditional Access policy that’s blocking the request.
Often, simply toggling the "Selected Apps" list in the "App Registrations" section of the portal fixes everything. You have to ensure the client ID of the app being used is authorized to act as a delegate.
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Actionable Next Steps
To get past this error and stay past it, follow this hierarchy of fixes:
- Audit your accounts: Ensure you aren't signed into multiple accounts that might be "fighting" for the delegate role on one app.
- Refresh the Token: Sign out and sign back in. It’s a cliché for a reason—it resets the OAuth handshake.
- Update the Software: If you are using an older version of Outlook (2016 or earlier) or an outdated macOS, the security protocols might simply be incompatible with the server's new requirements.
- Check Delegate Settings: In Outlook, go to File > Account Settings > Delegate Access. Ensure the permissions listed there actually match what you are trying to do.
- Clear the Cache: Delete stored passwords in your system's credential manager to remove any "stale" delegate data.
The "service delegate" isn't an enemy; it’s a gatekeeper. Usually, it’s just holding an old ID card for you and needs a new one. Update those credentials, align your permissions, and the gate will open.