I recently set up an email client (cant remember which one) for some friends on their laptop - using Sky email. I did this at my home (I'm not on Sky ISP (yet - moving to Sky next week)) & it worked just fine. The settings were as per the general setup - ie SMTP requires authentication & I used IMAP as the incoming rather than POP3 & everything required encryption.
When they got their laptop home the email client wouldn't connect to the Sky email servers & I went to fix it a week later. After much messing about, I discovered that by defining the port number with colon notation after the IP address - ie IP:port
it would work. When I again tried it at my house I was able to remove the ort
and it worked just fine without it defined (or with so re-added it). Seems that for that particular setup you need the ports defined but only within Sky's own network.