Can't connect to Freenet.de

I’m trying to replace Windows Mail with Mailspring, because I don’t want to use Outlook new.
For the most part it is ok, but I can’t get access to freenet.de.
I’ve tested different email clients, and they usually don’t have issues accessing it using IMAP/SMTP with SSL/TLS on ports IMAP:993 and SMTP:465, but nothing works with Mailspring.
I’m getting this error when using SSL (view log):
----------IMAP----------
connect mailcore::IMAPSession:004FFA9C
ssl connect mx.freenet.de 993 6
connect error 6

Any idea what I can do to correct the issue?

Thanks