Do Tiscali not offer an IMAP option?
I've done a little digging, are you in the UK? I'm not familiar with Tiscali, is it something to do with CPW's Talk Talk?
Anyway, try these IMAP settings...
imap.tiscali.co.uk - port 143 - no security
smtp.tiscali.co.uk - port 25 - no security
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