When you open the IONOS webmail on a Monday morning, enter your password, and nothing happens. Blank page, certificate error message, or infinite loading loop. Before adjusting the IMAP or SMTP settings, the first thing to do is to check if the problem is actually on our side or if there is a global outage of the 1&1 email service.
IONOS Status Page: The Reflex That Saves Time
IONOS provides a dedicated status page (ionos-status.fr) that reports in real-time any ongoing incidents with its mail, webmail, IMAP, and SMTP services. When the connection fails, checking this page before making any changes takes just a few seconds and can prevent you from altering a configuration that is working perfectly.
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We’ve all had that instinct to delete an email account in Outlook or Thunderbird to recreate it, while the IONOS server was simply undergoing maintenance. If the status page indicates an active incident with the email service, the only thing to do is wait for the resolution. In the meantime, you can test access from another network (mobile hotspot, for example) to confirm that the issue is not local.
When the status page shows no incidents, the issue lies with the browser, email client, or local network. This is where the technical checks begin.
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To resolve a 1&1 mail connection issue in this scenario, we move on to the diagnostic steps described below.
Antivirus and HTTPS Inspection: The Invisible Cause of Email Connection Errors
This is probably the most underestimated problem. Several popular antivirus programs (Avast, Kaspersky, Bitdefender) intercept HTTPS connections for analysis, including those to mail.ionos.fr. This mechanism, known as HTTPS inspection or mail protection, regularly causes SSL certificate errors, blank pages, or connection loops on the webmail.
The test is simple and quick: temporarily disable mail protection or HTTPS scanning in the antivirus settings, then try to reconnect. If the webmail opens normally, you’ve found the source of the problem.
What to Do Once the Cause is Identified
Two concrete options are available:
- Add mail.ionos.fr and the IONOS IMAP/SMTP servers to the antivirus HTTPS exclusion list, allowing you to maintain protection on other sites while freeing up the mail connection.
- Only disable the mail scanning module in the antivirus (often called “Mail Shield” or “Mail Protection”), keeping the rest of the security suite active.
- Check that the firewall integrated into the antivirus is not blocking the ports used by IONOS (993 for IMAP SSL, 587 for SMTP with STARTTLS).
Feedback varies on this point: some users resolve the issue in a minute with the exclusion, while others also need to clear the certificate cache of their browser. On Firefox, this option can be accessed via Settings, Privacy & Security, then Certificates.
IONOS IMAP and SMTP Settings: Common Configuration Errors on Outlook and Thunderbird
When configuring a 1&1 IONOS account on an email client, just one incorrect value in the server settings can block the connection. The problem often resurfaces after an Outlook update or a version change in Thunderbird that resets certain settings.
Server Settings to Check First
Here are the values to systematically check:
| Protocol | Server | Port | Encryption |
|---|---|---|---|
| IMAP (incoming) | imap.ionos.fr | 993 | SSL/TLS |
| SMTP (outgoing) | smtp.ionos.fr | 587 | STARTTLS |
The most common error concerns the SMTP port. Many outdated guides indicate port 465 with SSL, which still works in some cases but causes sending failures on recent configurations. Port 587 with STARTTLS is the setting recommended by IONOS and the one that poses the least compatibility issues.
Login ID: The Full Email Address
In both Outlook and Thunderbird, the username must be the full email address ([email protected]), not just the part before the @ symbol. This error generates a silent authentication refusal: the email client displays “incorrect password” even though the password is correct.
After any changes to the settings, restart the email client before retesting. Outlook in particular caches failed connection attempts and does not immediately retry with the new settings.
Synchronization Issue Between 1&1 IONOS and Outlook: The Case of Emails Received on Mobile but Not on PC
This scenario regularly appears in forums: messages are received on the mobile app, but Outlook on PC no longer synchronizes or retrieves emails with a delay of several hours. The problem often arises from a conflict between POP and IMAP connection modes.
In POP, the first device that connects “retrieves” the messages and can delete them from the server. If the phone is configured in POP and downloads the emails before Outlook, the latter finds nothing to retrieve. Switching all devices to IMAP resolves most synchronization issues since messages remain on the server and synchronize in real-time across each client.
To check the mode used in Outlook: File, then Account Settings. The “Type” column displays IMAP or POP. If a device is still in POP, the account needs to be deleted and recreated in IMAP with the settings from the table above.
Lastly, check the size of the inbox on the IONOS server if synchronization remains slow despite switching to IMAP: an inbox nearing its storage limit significantly slows down synchronization and can cause reception errors. Cleaning up old messages or upgrading to a plan with more storage space will then resolve the issue.