Actually,
secure.runbox.com is listed on the help pages:
http://www.runbox.com/twiki/bin/view/RunboxHelp/IMAP
Code:
IMAP setup information
* Incoming server type: IMAP
* Incoming mail server: imap.runbox.com
o For SSL, use secure.runbox.com.
* IMAP server port number: 143
o For SSL, use port 993.
I've heard people say that Runbox SSL is slower so I'm guessing that a 30 second timeout is too short. That would explain why sometimes it works and sometimes it doesn't.
You might try changing to the non-SSL connection and see if that helps.
Regards,
Rich