How to use operamail from behind a proxy?

How to use operamail from behind a proxy?

"2 cases here:
- at home, I can use operamail to fetch email from... let's say gmail's IMAP server
- at work, I'm behind a proxy, and when I tried to use operamail to fetch emails, it failed with the generic message 'The connection with the IMAP server was unexpectedly interrupted.'"