Your IONOS mailbox refuses to connect, your emails are not arriving, or Outlook displays a looping authentication error. These situations occur regularly and almost always have a specific technical explanation. Before contacting support, a few methodical checks can resolve the majority of blocks on the IONOS webmail or email client.
IONOS Server Outages: Check Before Looking on the User Side
Have you already spent an hour modifying your IMAP settings with no results? The problem may have come from the server itself. IONOS documents its incidents on national status pages, including ionos-status.fr for France. These pages occasionally confirm specific outages on mail systems that prevent the sending or receiving of messages.
The reflex to adopt: check this status page before making any changes. If an incident is ongoing, modifying your connection settings will not change anything and may even complicate recovery once the service is restored.
A detailed guide explains what to do in case of IONOS mail issues when a bug persists despite basic checks. The recommended approach is to isolate the source of the malfunction (server, client, configuration) before taking action.
Outlook Authentication Error and Autodiscover Conflict
Outlook is the email client that generates the most conflicts with IONOS accounts. The reason lies in a feature called Autodiscover. This mechanism, designed to automatically configure Microsoft 365 accounts, conflicts with the IONOS configuration when both coexist on the same machine.
The Windows Credential Manager, an Unknown Trap
Windows stores the login credentials of your email accounts in memory. When you change an IONOS password or add a new account, the old credentials remain cached and cause authentication loops. Outlook repeatedly asks for the password without ever accepting the correct one.
To resolve this blockage, open the Windows Credential Manager (accessible via the Control Panel), then delete all entries related to IONOS or Exchange. Restart Outlook. In most cases, the connection is restored immediately.
Disable Autodiscover for Microsoft 365
IONOS now recommends explicitly disabling Autodiscover for Microsoft 365 in Outlook settings. Once this option is turned off, Outlook offers IONOS Autodiscover. Accept it, check “Don’t ask again,” and the connection stabilizes.
This recent manipulation shows that the problem does not stem from a wrong password, but from a conflict between two automatic configuration systems that interfere with each other.
IMAP and SMTP Settings: The Most Common Input Errors
When the connection fails on a smartphone or a client like Thunderbird, the problem often comes from a wrongly entered setting. The values to use for an IONOS email account are precise, and a single mistake is enough to block sending or receiving.
Here are the points to systematically check:
- IMAP Incoming Server: the address must exactly match the one indicated in the IONOS customer area, with the port and SSL/TLS encryption enabled. An incorrect port (for example, 143 instead of 993) blocks the connection without a clear error message.
- SMTP Outgoing Server: same logic, the secure SMTP port and authentication must be enabled. Without SMTP authentication, the server refuses to send even if receiving works.
- Login ID: on IONOS, the ID is the full email address (with the domain), not just a username. Entering only the part before the @ results in an immediate rejection.
- Password: the one defined in the IONOS customer area, not the webmail one if you modified it separately. The two can become desynchronized.
After correcting, remove the account from the email client and recreate it properly. Modifying an existing account does not always purge the connection cache.
Emails Missing from the IONOS Inbox: Spam Folder and Filtering Rules
Your emails are arriving on the server but do not appear in your inbox. This scenario has two main causes.
The first: IONOS’s anti-spam filter classifies some legitimate messages as junk. Log in to IONOS webmail (not your email client) and check the spam folder. An email classified as spam on the server never appears in Outlook or Thunderbird if your client does not synchronize this folder.
The second: active filtering rules in the webmail automatically redirect certain messages to specific folders. These rules persist even when you change email clients. To check them, access the filtering settings in the IONOS webmail interface and temporarily disable all custom rules.
Storage Space Full
When the mailbox reaches its maximum capacity, the server silently rejects new messages. The sender sometimes receives a non-delivery notice, but not always. Check the space used in your IONOS customer area. If the mailbox is full, archive or delete old messages before emptying the trash (which also consumes quota).
Firewall, Antivirus, and Network Security: Invisible Blocks
Some security software intercepts encrypted email connections to analyze them. This feature, sometimes called “SSL scanning” or “email protection,” breaks the secure connection between your client and the IONOS server.
To identify this type of blockage:
- Temporarily disable your antivirus’s email scanning and test the connection. If it works, the problem is confirmed.
- Add IONOS servers as exceptions in your firewall or security suite.
- On a corporate network, check that the IMAP (993) and SMTP (465 or 587) ports are not blocked by the network firewall.
IONOS webmail operates via the browser on port 443 (HTTPS). If webmail works but your email client does not, the problem lies between your software and the network, not on the server side.
An IONOS mail issue is almost always resolved by first identifying whether the outage is on the server side, configuration side, or local network side. Starting with the status page, then checking IMAP/SMTP settings, and then examining filters and local security allows you to eliminate causes one by one without wasting time on false leads.