Hello,
I am experiencing a CalDAV synchronization issue with eM Client and I need your assistance.
— ENVIRONMENT —
- eM Client version: 10.4.5326+97a2e75a43 (Windows)
- OS: Windows 10
- CalDAV server: O2Switch hosting (Roundcube)
- CalDAV URL: https://4levelup.fr:2080/calendars/[email protected]/calendar/
— ERROR —
The synchronization fails with the following error:
MailClient.Accounts.ConnectionException: The SSL connection could not be established
—> System.Security.Authentication.AuthenticationException: Authentication failed
—> System.ComponentModel.Win32Exception (0x80090302): La fonction demandée n’est pas prise en charge
— WHAT I HAVE TRIED —
- Enabled TLS 1.2 and TLS 1.3 in Windows Internet Options
- Tested the URL directly in a browser (Edge) → the server responds correctly and displays a login page, so the SSL certificate is valid
- Switched the URL from HTTPS to HTTP → the server closes the connection immediately (error 10054), meaning it forces HTTPS
— CONCLUSION —
The server is working fine and the SSL certificate is valid. The issue seems to be a TLS negotiation incompatibility between eM Client and the server on port 2080. Google Calendar accounts synchronize without any issue, so the problem is specific to this CalDAV connection.
Could you please advise:
- Is there a known compatibility issue between eM Client and certain TLS configurations?
- Is there a way to force a specific TLS version in eM Client?
- Are there any additional diagnostic steps I can take?
Thank you for your support.
Best regards,
David Enée