Problem with Blueyonder servers and Mac Mail

I have experienced considerable difficulty in setting up my Blueyonder email account on my new MacBook Air running Mac Mail in Yosemite. After spending over eleven hours with very helpful second line technical support staff at Apple and Virgin Media (both companies wouldn't accept responsibility for the problem unsurprisingly!) I have been forced to the conclusion that I simply can't use Mac Mail and my Blueyonder account.

The problem was fixed by ditching Mac Mail in favour of a new Mail Client as the prospect of changing my email account (with all the consequent notifications to people/organisations set up to use my Blueyonder address) was too depressing!

I firstly used 'Inky' which is free and really easy to set up as it finds the servers and ports for you and (only because I didn't like Inky's layout) I bought 'Postbox' (available on a 30 day free trial) which looks almost identical to Mac Mail, finds the servers and ports for you and has a number of really useful additional features that I'm currently exploring.

Has anybody else experienced this incompatibility problem and, if so, was there a fix I missed?