Outlook no longer allows me to access my Microsoft Exchange email account from IONOS

Question

I have a Microsoft 365 personal subscription. I've had it for several year. I also have an IONOS (previous 1and1) Microsoft Exchange 2019 email account. Everything was working exactly how it should until around October 25, 2025. Since then, I can't access my IONOS MS Exchange email in the Outlook desktop apps. I know it is not my IONOS account because I am still receiving my email on my iPhone (in the Outlook app) and on my iPad Pro (in the Mail app). It is specific to the Outlook desktop apps on my Microsoft Surface and my Microsoft Surface Go. It just stopped working. I have tried removing profiles, deleting data, deleting emails, and uninstalled and reinstalled MS 365 several times trying to start over from scratch. I have tried to manually set up my IONOS MS Exchange 2019 email but Outlook has commandeered my email and rerouted it to an outlook.com email and is not letting me reset it to the real email address. Of course I can't find a way to contact anyone at Microsoft to help me with this. Outlook is a major reason I purchased the subscription. I am now going on two weeks without it. This is absolutely unacceptable that just out of the blue it stops working and no longer allows me to use it. I have not changed passwords. I made no changes in the date leading up to when it stopped. I don't understand why no one can help me with this.

Answer 1

Hi Chad and others - I've been struggling with this IONOS Exchange email problem for a while, but solved it yesterday with a combination of IONOS tech support and Copilot. I'll paste below the solution that worked for me. In essence, Microsoft is hijacking the IONOS autodiscover process (which is a bit unusual to be fair) to a wrong address and causing existing Exchange accounts hosted by IONOS to fail to connect. And if you delete the email account and try to re-add it, or make a new profile to add your email account, it fails. Don't be sidetracked by the fact that IONOS, without telling us, changed their exchange email server from exchange2019.ionos.co.uk to exchange.ionos.co.uk - the whole process of adding an email account works fine automatically via Autodiscover. Relevant bits pasted below - it's Copilot talking, not me, after it reviewed IONOS tech support advice. As I said, it worked for me on two PCs, and although I can't guarantee it will work for others, trying it will do no harm.

Step 1. Check Autodiscover Resolution (DNS & Hosts File)

Use PowerShell to Check DNS Resolution

This will show you where autodiscover.yourdomain.com is pointing.

1.1           Open PowerShell (as Administrator if possible).

1.2           Run this command (replace with your actual domain):

Resolve-DnsName autodiscover.yourdomain.com

1.3           Look at the "Name" and "IP Address" or "CNAME" in the results.

•             If you see something like:

Name: autodiscover.yourdomain.com

CNAME: adsredir.ionos.info

✅ That’s correct.

•             If it points to something like autodiscover.outlook.com or another provider, that’s likely the issue.

Step 2 (presuming Step 1 returns the CNAME above)

Cleanup (Non-invasive). These steps don’t touch the registry but can help isolate the issue:

2.1. Clear Outlook Autodiscover Cache - Outlook caches Autodiscover responses in XML files.

•             In file manager, navigate to:

%LOCALAPPDATA%\Microsoft\Outlook

•             Delete any files which include in the name:

....Autodiscover.xml

New Autodiscover.xml file(s) will be created automatically later

Step 3. Apply the Registry Fix

IONOS already suggested this, and your symptoms match the scenario it’s designed to fix.

🛠️ Registry Fix: Disable Microsoft 365 Autodiscover Fallback

🔹 Step 3.1: Open Registry Editor

• Press Windows + R, type regedit, and hit Enter.
• If prompted by UAC, click Yes.

🔹 Step 3.2: Navigate to the First Registry Path

Go to (paste it into the address bar at the top):

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover

If any folder in the path doesn’t exist, you can right-click and create it manually as a new 'key'.

🔹 Step 3.3: Add the DWORD

1.           Right-click in the right pane → New > DWORD (32-bit) Value

2.           Name it (or rename it via a right click):

ExcludeExplicitO365Endpoint

3.           Double-click it and set Value data to: 1

🔹 Step 3.4: Repeat in Policies Path

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\AutoDiscover

Again, create missing folders if needed [note from Hans: I had to create the lower folders in this path for the second registry edit]

Repeat the same steps:

•             Add: ExcludeExplicitO365Endpoint as a DWORD

•             Set its value to 1

🔹 Step 3.5: Reboot

Restart your PC to ensure the registry changes take effect.

After Reboot, delete any new Autodiscover.xml files again.

Step 4. ✅ Implement the Correct Setup Path (Autodiscover-driven)

To connect Outlook to IONOS Exchange, you must let Autodiscover do the work. Here’s how:

🔹 Use the “Add Account” Wizard via control panel — No Manual Server Entry:

·         Go to Control Panel > Mail > Show Profiles > Add

·         Create a new profile

·         Choose Email Account (not manual setup)

·         Enter:

•             Your name

•             Your full email address

•             Your password

5.           Click Next and let Outlook run Autodiscover

If Autodiscover is working correctly (and the registry fix is in place), Outlook should find the correct Exchange server and configure MAPI over HTTP — not EAS.

Open Outlook to check that the account works and the mail folders are repopulating (can take some time if there are a lot of messages on the server)

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Answer 2

It sounds like you're experiencing a frustrating issue with accessing your IONOS Microsoft Exchange email account through Outlook on your desktop devices. Here are a few troubleshooting steps you can try:

1. Check for Software Updates: Ensure that both your Windows operating system and Outlook application are up to date. Outdated software can often lead to connectivity issues.
2. Run Microsoft 365 Diagnostics: If you have admin access, you can run the Microsoft 365 diagnostics to check for any connectivity problems. This tool can help identify issues and suggest solutions.
3. Reset the Hosts File: Sometimes, incorrect entries in the Hosts file can prevent Outlook from connecting to the Exchange server. Make sure to reset the Hosts file on your devices to ensure that DNS is used for resolving the server names.
4. Manual Configuration: Since you mentioned that Outlook is redirecting to an outlook.com email, try manually configuring your IONOS email account in Outlook. Make sure to use the correct server settings for IONOS Exchange 2019.
5. Check for Service Issues: If multiple users in your organization are experiencing similar issues, it could be a service-related problem. You can check the Microsoft 365 Service health status for any ongoing issues.

If these steps do not resolve the issue, you may want to consider reaching out to Microsoft support for further assistance, as they can provide more specific guidance based on your account and setup.

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References:

• Connection to Microsoft Exchange is unavailable error when a Microsoft 365 user tries to set up Outlook
• Fix Outlook connection problems for Microsoft 365 account
• Microsoft 365 users can't connect to Exchange Online because of incorrect service settings