Vista Outlook and emails from webhosting uk

[SevenCentSkill]

Hi, one of my customers is having a peculiar problem with recieving emails on Vista, I went over and checked it out, its a cerrtificate error with tristar, because vista seems to take issues with email coming from there while his domain name is different to the name in the certificate, I tried everything to get it to accept the certificate permanently, as if you accept temporarily it goes away for that session, but it wasn't playing ball. Is there anything I can do from the clients Cpanel to help with this? It seems local to vista, though I did used to get a similar one in Thunderbird on XP a while ago, havent seen that for a while though.