It surprises me that there is nobody posting problems with email on these boards. A different forum is littered with them.
As sky is very much a plug and play ISP, with preconfigured routers and install CD's, I am surprised they have completely changed POP and SMTP details, and then changed everyone over on the same day!
The imap thing would bug me, if I used my @sky.com account.
Pipex -> Zen -> UKFSN -> Sky LLU